# 5.5E: Exercises

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## Practice Makes Perfect

Solve Mixture Applications

In the following exercises, translate to a system of equations and solve.

Peter has been saving his loose change for several days. When he counted his quarters and dimes, he found they had a total value $13.10. The number of quarters was fifteen more than three times the number of dimes. How many quarters and how many dimes did Peter have? Answer Peter had 11 dimes and 48 quarters. ##### Exercise $$\PageIndex{10}$$ Lucinda had a pocketful of dimes and quarters with a value of$ $6.20. The number of dimes is eighteen more than three times the number of quarters. How many dimes and how many quarters does Lucinda have? ##### Exercise $$\PageIndex{11}$$ A cashier has 30 bills, all of which are$10 or $20 bills. The total value of the money is$460. How many of each type of bill does the cashier have?

The cashier has fourteen $10 bills and sixteen$20 bills.

A cashier has 54 bills, all of which are $10 or$20 bills. The total value of the money is $910. How many of each type of bill does the cashier have? ##### Exercise $$\PageIndex{13}$$ Marissa wants to blend candy selling for$1.80 per pound with candy costing $1.20 per pound to get a mixture that costs her$1.40 per pound to make. She wants to make 90 pounds of the candy blend. How many pounds of each type of candy should she use?

Marissa should use 60 pounds of the $1.20/lb candy and 30 pounds of the$1.80/lb candy.

How many pounds of nuts selling for $6 per pound and raisins selling for$3 per pound should Kurt combine to obtain 120 pounds of trail mix that cost him $5 per pound? ##### Exercise $$\PageIndex{15}$$ Hannah has to make twenty-five gallons of punch for a potluck. The punch is made of soda and fruit drink. The cost of the soda is$1.79 per gallon and the cost of the fruit drink is $2.49 per gallon. Hannah’s budget requires that the punch cost$2.21 per gallon. How many gallons of soda and how many gallons of fruit drink does she need?

Hannah needs 10 gallons of soda and 15 gallons of fruit drink.

Joseph would like to make 12 pounds of a coffee blend at a cost of $6.25 per pound. He blends Ground Chicory at$4.40 a pound with Jamaican Blue Mountain at $8.84 per pound. How much of each type of coffee should he use? ##### Exercise $$\PageIndex{17}$$ Julia and her husband own a coffee shop. They experimented with mixing a City Roast Columbian coffee that cost$7.80 per pound with French Roast Columbian coffee that cost $8.10 per pound to make a 20 pound blend. Their blend should cost them$7.92 per pound. How much of each type of coffee should they buy?

Julia and her husband should buy 12 pounds of City Roast Columbian coffee and 8 pounds of French Roast Columbian coffee.

Melody wants to sell bags of mixed candy at her lemonade stand. She will mix chocolate pieces that cost $4.89 per bag with peanut butter pieces that cost$3.79 per bag to get a total of twenty-five bags of mixed candy. Melody wants the bags of mixed candy to cost her $4.23 a bag to make. How many bags of chocolate pieces and how many bags of peanut butter pieces should she use? ##### Exercise $$\PageIndex{19}$$ Jotham needs 70 liters of a 50% alcohol solution. He has a 30% and an 80% solution available. How many liters of the 30% and how many liters of the 80% solutions should he mix to make the 50% solution? Answer Jotham should mix 42 liters of the 30% solution and 28 liters of the 80% solution. ##### Exercise $$\PageIndex{20}$$ Joy is preparing 15 liters of a 25% saline solution. She only has 40% and 10% solution in her lab. How many liters of the 40% and how many liters of the 10% should she mix to make the 25% solution? ##### Exercise $$\PageIndex{21}$$ A scientist needs 65 liters of a 15% alcohol solution. She has available a 25% and a 12% solution. How many liters of the 25% and how many liters of the 12% solutions should she mix to make the 15% solution? Answer The scientist should mix 15 liters of the 25% solution and 50 liters of the 12% solution. ##### Exercise $$\PageIndex{22}$$ A scientist needs 120 liters of a 20% acid solution for an experiment. The lab has available a 25% and a 10% solution. How many liters of the 25% and how many liters of the 10% solutions should the scientist mix to make the 20% solution? ##### Exercise $$\PageIndex{23}$$ A 40% antifreeze solution is to be mixed with a 70% antifreeze solution to get 240 liters of a 50% solution. How many liters of the 40% and how many liters of the 70% solutions will be used? Answer 160 liters of the 40% solution and 80 liters of the 70% solution will be used. ##### Exercise $$\PageIndex{24}$$ A 90% antifreeze solution is to be mixed with a 75% antifreeze solution to get 360 liters of a 85% solution. How many liters of the 90% and how many liters of the 75% solutions will be used? Solve Interest Applications In the following exercises, translate to a system of equations and solve. ##### Exercise $$\PageIndex{25}$$ Hattie had$3,000 to invest and wants to earn 10.6% interest per year. She will put some of the money into an account that earns 12% per year and the rest into an account that earns 10% per year. How much money should she put into each account?

Hattie should invest $900 at 12% and$2,100 at 10%.

Carol invested $2,560 into two accounts. One account paid 8% interest and the other paid 6% interest. She earned 7.25% interest on the total investment. How much money did she put in each account? ##### Exercise $$\PageIndex{27}$$ Sam invested$48,000, some at 6% interest and the rest at 10%. How much did he invest at each rate if he received $4,000 in interest in one year? Answer Sam invested$28,000 at 10% and $20,000 at 6%. ##### Exercise $$\PageIndex{28}$$ Arnold invested$64,000, some at 5.5% interest and the rest at 9%. How much did he invest at each rate if he received $4,500 in interest in one year? ##### Exercise $$\PageIndex{29}$$ After four years in college, Josie owes$65,800 in student loans. The interest rate on the federal loans is 4.5% and the rate on the private bank loans is 2%. The total interest she owed for one year was $2,878.50. What is the amount of each loan? Answer The federal loan is$62,500 and the bank loan is $3,300. ##### Exercise $$\PageIndex{30}$$ Mark wants to invest$10,000 to pay for his daughter’s wedding next year. He will invest some of the money in a short term CD that pays 12% interest and the rest in a money market savings account that pays 5% interest. How much should he invest at each rate if he wants to earn $1,095 in interest in one year? ##### Exercise $$\PageIndex{31}$$ A trust fund worth$25,000 is invested in two different portfolios. This year, one portfolio is expected to earn 5.25% interest and the other is expected to earn 4%. Plans are for the total interest on the fund to be $1150 in one year. How much money should be invested at each rate? Answer$12,000 should be invested at 5.25% and $13,000 should be invested at 4%. ##### Exercise $$\PageIndex{32}$$ A business has two loans totaling$85,000. One loan has a rate of 6% and the other has a rate of 4.5%. This year, the business expects to pay $4650 in interest on the two loans. How much is each loan? ## Everyday Math In the following exercises, translate to a system of equations and solve. ##### Exercise $$\PageIndex{33}$$ Laurie was completing the treasurer’s report for her son’s Boy Scout troop at the end of the school year. She didn’t remember how many boys had paid the$15 full-year registration fee and how many had paid the $10 partial-year fee. She knew that the number of boys who paid for a full-year was ten more than the number who paid for a partial-year. If$250 was collected for all the registrations, how many boys had paid the full-year fee and how many had paid the partial-year fee?

14 boys paid the full-year fee. 4 boys paid the partial-year fee

As the treasurer of her daughter’s Girl Scout troop, Laney collected money for some girls and adults to go to a three-day camp. Each girl paid $75 and each adult paid$30. The total amount of money collected for camp was $765. If the number of girls is three times the number of adults, how many girls and how many adults paid for camp? ## Writing Exercises ##### Exercise $$\PageIndex{35}$$ Take a handful of two types of coins, and write a problem similar to Example relating the total number of coins and their total value. Set up a system of equations to describe your situation and then solve it. Answer Answers will vary. ##### Exercise $$\PageIndex{36}$$ In Example we solved the system of equations $$\left\{\begin{array}{l}{b+f=21,540} \\ {0.105 b+0.059 f=1669.68}\end{array}\right.$$ by substitution. Would you have used substitution or elimination to solve this system? Why? ## Self Check a. After completing the exercises, use this checklist to evaluate your mastery of the objectives of this section. b. After looking at the checklist, do you think you are well-prepared for the next section? Why or why not? ## More Practice: Money Problems ##### Exercise $$\PageIndex{37}$$ 1. Two families bought tickets for the home basketball game. One family ordered $$2$$ adult tickets and $$4$$ children’s tickets for a total of $$36.00$$. Another family ordered $$3$$ adult tickets and $$2$$ children’s tickets for a total of $$32.00$$. How much did each ticket cost? 2. Two friends found shirts and shorts on sale at a flea market. One bought $$4$$ shirts and $$2$$ shorts for a total of $$28.00$$. The other bought $$3$$ shirts and $$3$$ shorts for a total of $$30.75$$. How much was each shirt and each pair of shorts? 3. A community theater sold $$140$$ tickets to the evening musical for a total of $$1,540$$. Each adult ticket was sold for $$12$$ and each child ticket was sold for $$8$$. How many adult tickets were sold? 4. The campus bookstore sells graphing calculators for $$110$$ and scientific calculators for $$16$$. On the first day of classes $$50$$ calculators were sold for a total of $$1,646$$. How many of each were sold? 5. Jim was able to purchase a pizza for $$12.35$$ with quarters and dimes. If he uses $$71$$ coins to buy the pizza, then how many of each did he have? 6. A cash register contains $$5$$ bills and $$10$$ bills with a total value of $$350$$. If there are $$46$$ bills total, then how many of each does the register contain? 7. A jar consisting of only nickels and quarters contains $$70$$ coins. If the total value is $$9.10$$, how many of each coin are in the jar? 8. Jill has $$9.20$$ worth of dimes and quarters. If there are $$68$$ coins in total, how many of each does she have? Answer 1. Adults $$7.00$$ each and children $$5.50$$ each. 3. $$105$$ adult tickets were sold. 5. $$35$$ quarters and $$36$$ dimes 7. The jar contains $$42$$ nickels and $$28$$ quarters ## More Practice: Combined fixed and variable costs A taxi fare includes a fixed flat fee, plus a variable cost that depends on the number of miles driven. Total manufacturing costs include a fixed overhead cost, plus a variable cost that depends on the number of items manufactured. ##### Exercise $$\PageIndex{38}$$ 1. In a moderate-size city, taxi fare is$51 for 12 miles and is $31 for 7 miles. What is the flat fee and what is the charge per mile? 2. If it costs$90 to rent a car driven 100 miles and $140 for one driven 200 miles, find the daily rental fee and the mileage fee. 3. To manufacture 30 items, it costs$2700, and to manufacture 50 items, it costs $3200. Find the overhead cost and the cost to manufacture one item 4. To manufacture 100 items, it costs$32,000, and to manufacture 200 items, it costs $40,000. Find the overhead cost and the cost to manufacture one item 5. If it costs a total of$750 to produce 20 items and the cost to manufacture an item is $25, what is the overhead cost? 6. If it costs$1900 to manufacture 60 items, and the overhead is \$700, what is the cost to produce one item?
7. Sally earns $$1,000$$ per month plus a commission of $$2$$% of sales. Jane earns $$200$$ per month plus $$6$$% of her sales. At what monthly sales figure will both Sally and Jane earn the same amount of pay?
8. The cost of producing specialty book shelves includes a daily production cost plus an additional cost per book shelf. The cost to produce 7 book shelves in 2 days was $$590$$. The cost to produce 11 book shelves in 3 days was $$910$$. Find the daily cost and the cost for one bookshelf.

1.  $$\ 4$$ per mile     3.    $$\ 25$$ per item;  $$\ 1950$$ overhead costs.      5.  $$\ 250$$ overhead     7.  Sales of $$20,000$$.

## More Practice: Percent Solution Problems

##### Exercise $$\PageIndex{39}$$

Set up a linear system and solve.

1. A $$17$$% acid solution is to be mixed with a $$9$$% acid solution to produce $$8$$ gallons of a $$10$$% acid solution. How much of each is needed?

2. A nurse wishes to obtain $$28$$ ounces of a $$1.5$$% saline solution. How much of a $$1$$% saline solution must she mix with a $$4.5$$% saline solution to achieve the desired mixture?

3. A customer ordered $$4$$ pounds of a mixed peanut product containing $$12$$% cashews. The inventory consists of only two mixes containing $$10$$% and $$26$$% cashews. How much of each type must be mixed to fill the order?

4. One alcohol solution contains $$10$$% alcohol and another contains $$25$$% alcohol. How much of each should be mixed together to obtain $$2$$ gallons of a $$13.75$$% alcohol solution?

5. A $$50$$% fruit juice concentrate can be purchased wholesale. Best taste is achieved when water is mixed with the concentrate in such a way as to obtain a $$15$$% fruit juice mixture. How much water and concentrate is needed to make a $$60$$-ounce fruit juice drink?

6. How much cleaning fluid concentrate, with $$60$$% alcohol content, must be mixed with water to obtain a $$24$$-ounce mixture with $$15$$% alcohol content?

7. How many pounds of pure peanuts must be combined with a $$20$$% peanut mix to produce $$2$$ pounds of a $$50$$% peanut mix?

8. Pure sugar is to be mixed with a fruit salad containing $$10$$% sugar to produce $$63$$ ounces of a salad containing $$18$$% sugar. How much pure sugar is required?

9. A custom aluminum alloy is created by mixing $$150$$ grams of a $$15$$% aluminum alloy and $$350$$ grams of a $$55$$% aluminum alloy. What percentage of aluminum is in the resulting mixture?

10.A research assistant mixed $$500$$ milliliters of a solution that contained a $$12$$% acid with $$300$$ milliliters of water. What percentage of acid is in the resulting solution?

1. $$7$$ gallons of the $$9$$% acid solution and $$1$$ gallon of the $$17$$% acid solution

3. $$3.5$$ pounds of the $$10$$% cashew mix and $$0.5$$ pounds of the $$26$$% cashew mix

5. $$18$$ ounces of fruit juice concentrate and $$42$$ ounces of water

7. $$.75$$ pounds of pure peanuts

9. $$43$$%.

## More Practice: Per Cent Interest

##### Exercise $$\PageIndex{40}$$
1. A $$5,200$$ principal is invested in two accounts, one earning $$3$$% interest and another earning $$6$$% interest. If the total interest for the year is $$210$$, then how much is invested in each account?
2. Harry’s $$2,200$$ savings is in two accounts. One account earns $$2$$% annual interest and the other earns $$4$$%. His total interest for the year is $$69$$. How much does he have in each account?
3. Janine has two savings accounts totaling $$6,500$$. One account earns $$2 \frac{3}{4}$$% annual interest and the other earns $$3 \frac{1}{2}$$%. If her total interest for the year is $$211$$, then how much is in each account?
4. Margaret has her total savings of $$24,200$$ in two different CD accounts. One CD earns $$4.6$$% interest and another earns $$3.4$$% interest. If her total interest for the year is $$1,007.60$$, then how much does she have in each CD account?
5. Last year Mandy earned twice as much interest in her Money Market fund as she did in her regular savings account. The total interest from the two accounts was $$246$$. How much interest did she earn in each account?
6. A small business invested $$120,000$$ in two accounts. The account earning $$4$$% annual interest yielded twice as much interest as the account earning $$3$$% annual interest. How much was invested in each account?
1. $$3,400$$ at $$3$$% and $$1,800$$ at $$6$$%
3. $$2,200$$ at $$2 \frac{3}{4}$$% and $$4,300$$ at $$3 \frac{1}{2}$$%
5. Savings: $$82$$; Money Market: $$164$$.