Title: Lesson 4-4
Author: mark_cameron
Last saved by: MHE
Company: McGraw-Hill

Lesson 4-3

Example 1 Write and Solve a Proportion
WEATHER During the first 2 hours of a winter storm, a total of 3 inches of snow had fallen. Write and solve a proportion to find the amount of time it will take at this rate for an additional 4 inches of snow to fall.

Write a proportion. Let t represent the time in hours.

    		Write the proportion.
  		Find the cross products.
    3t = 8		Multiply.
   		Divide each side by 3.
      		Simplify.

It will take  hours, or 2 hours 40 minutes, for an additional 4 inches of snow to fall.

Example 2 Real-World Example
MANUFACTURING A quality control manager randomly tests some flashlights as they come off an assembly line. She finds 5 flashlights with defects and 195 flashlights with no defects. How many defective flashlights should she expect to find in a production run of 10,000 flashlights?

     or 

Write a proportion. Let d represent the number of defective flashlights in a production run of 10,000.

           		Write the proportion.
  		Find the cross products.
     10,000 = 40d		Multiply.
     		Divide each side by 40.
          		Simplify.

The quality control manager should expect to find 250 defective flashlights in a production run of 10,000.

Example 3 Write and Use an Equation
SHOPPING Kaylee bought 3 pounds of cashews for $23.85. Write an equation relating the cost to the number of pounds of cashews. How much would Kaylee pay for 2 pounds of cashews at this same rate? for 5 pounds?

Find the constant of proportionality between cost and pounds.

 or 7.95		The cost is $7.95 per pound.

Words	The cost is $7.95 times the number of pounds.
Variables	Let c represent the cost.
	Let p represent the number of pounds.
Equation	c = 7.95  p

Use this same equation to find the cost for 2 and 5 pounds of cashews sold at the same rate.

c = 7.95p | | Write the equation. | | c = 7.95p
c = 7.95(2) | | Replace p with the number of pounds. | | c = 7.95(5)
c = 15.90 | | Multiply. | | c = 39.75

The cost for 2 pounds of cashews is $15.90 and for 5 pounds is $39.75.