Direct and Inverse Variation Practice



Alg 2 A Day 13 – Inverse Variation

Unit 3

Review: If “y varies DIRECTLY as x”, then ___________________________________________.

New Info: If “y varies INVERSELY as x”, then __________________________________________.

Example: If y varies INVERSELY as x and y = 4 when x = 3, then find y when x = 2.

Step 1: Set-up equation:

Step 2: Fill in values of the variables and solve for k.

Step 3: Rewrite the equation, with the value of “k”.

Step 4: Answer the question being asked.

Solve each problem below. You can use the 4 steps above for both DIRECT and INVERSE variation.

1. y varies directly as x and y = 14 when x = 3.5. Find y when x = 21.

2. y varies inversely as x and y = 3 when x = 8. Find x when y = 12.

3. The circumference of a circle varies directly as the radius and C = 7[pic]feet when

r = 3.5 feet. Find r when C = 4.5[pic]feet.

4. The time it takes a Joe, Markeya and a group of other volunteers to build a house varies inversely with the number of volunteers. If 20 volunteers can build a house in 62.5 hours, how many volunteers would be needed to build a house in 50 hours?

5. The wavelength of a certain radio wave varies directly as the velocity of the wave. If the wavelength is 60 feet when the velocity of the wave is 15 feet per second, find the wavelength when the velocity is 3 feet per second.

6. The dollar amount, d, that Laura earns varies directly with the number of hours, t that she works. If d = $116.25 when t = 15, find t when d = $178.25.

7. The time it takes Scott to drive a certain distance varies inversely with the average speed of his car. It takes 4.75 hours to travel between 2 cities at 60 miles per hour. How long would it take Scott to do the same drive at 50 miles per hour?

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