# 3.1.1: Exercises - Linear Applications

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## PROBLEM SET: LINEAR APPLICATIONS

In the following application problems, assume a linear relationship holds.

 1) The variable cost to manufacture a product is $25 per item, and the fixed costs are$1200.  If x is the number of items manufactured and y is the cost, write the cost function. 2) It costs $90 to rent a car driven 100 miles and$140 for one driven 200 miles. If x is the number of miles driven and y the total cost of the rental, write the cost function. 3) The variable cost to manufacture an item is $20 per item, and it costs a total of$750 to produce 20 items. Define the unknowns and write the cost function. 4) To manufacture 30 items, it costs $2700, and to manufacture 50 items, it costs$3200. Define the unknowns and write the cost function. 5) To manufacture 100 items, it costs $32,000, and to manufacture 200 items, it costs$40,000. Define the unknowns and write the cost function. 6) It costs $1900 to manufacture 60 items, and the fixed costs are$700. Define the unknowns and write the cost function. 7) Mugs Café sells 1000 cups of coffee per week if it does not advertise. For every $50 spent in advertising per week, it sells an additional 150 cups of coffee. a) Find an equation that gives y = number of cups of coffee sold per week x = amount spent on advertising per week. b) How many cups of coffee does Mugs Café expect to sell if$100 per week is spent on advertising? 8) EZ Clean company has determined that if it spends $30,000 on advertising, it can hope to sell 12,000 of its Minivacs a year, but if it spends$50,000, it can sell 16,000. Write an equation that gives a relationship between the number of dollars spent on advertising (x) and the number of minivacs sold (y). 9) The cost of electricity in residential homes is a linear function of the amount of energy used. In Denver a home using 250 kilowatt hours (kwh) of electricity per month pays $55. A home using 600 kwh per month pays$118. Define the unknowns and write the cost of electricity as a function of the amount used. Then use the function to find the cost for a home using 400 kwh of electricity per month. 10) Using the equation from the previous problem, find the level of electricity use that would correspond to a monthly cost of $100. 11) It costs$1,200 to produce 50 pounds of a chemical and it costs $2,200 to produce 150 pounds. The chemical sells for$15 per pound. Define the unknowns and find the cost function. What is the fixed cost and what is the variable cost? How many pounds must be sold to break even? Find the cost and revenue at the break-even point. 12) Whackemhard Sports is planning to introduce a new line of tennis rackets. The fixed costs for the new line are $25,000 and the variable cost of producing each racket is$60. Define the unknowns and find the cost function. How many rackets must be sold to break even? Find the cost and revenue at the break-even point. 13) A demand curve for a product is the number of items the consumer will buy at different prices. At a price of $2 a store can sell 2400 of a particular type of toy truck. At a price of$8 the store can sell 600 such trucks. If x represents the price of trucks and y the number of items sold, write an equation for the demand curve. 14) A supply curve for a product is the number of items that can be made available at different prices. A manufacturer of toy trucks can supply 2000 trucks if they are sold for $8 each; it can supply only 400 trucks if they are sold for$4 each. If x is the price and y the number of items, write an equation for the supply curve. 15) The freezing temperatures for water for Celsius and Fahrenheit scales are 0ºC and 32ºF. The boiling temperatures for water are 100 ºC and 212 ºF. Let C denote the temperature in Celsius and F in Fahrenheit. Write the conversion function from Celsius to Fahrenheit. Then use the function to convert 25 ºC into ºF. 16) Using the same data as given in the previous problem, find a conversion function that converts Fahrenheit into Celsius.  Then use this conversion function to convert 72 ºF into an equivalent Celsius measure. 17) California’s population was 29.8 million in the year 1990, and 37.3 million in 2010. Assume that the population trend was and continues to be linear, write the population function. Use this function to predict the population in 2025. Hint: Use 1990 as the base year (year 0); then 2010 and 2025 are years 20, and 35, respectively.) 18) Use the population function for California in the previous problem to find the year in which the population will be 40 million people.

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