Writing and interpreting functions

If y varies directly with x, and y = 8 when x = 3, what is x when y = -56?

• 21

• -21

• -149.33

• 149.33

Write the variation equation: The number of square tiles (t) used to tile a floor varies inversely with the square of the length (l) of the tile.

•  $t\ =\ kl^2$  

•  $t^2=\frac{k}{l}$  

•  $t\ =\ \frac{k}{l^2}$  

•  $t^2=\frac{k}{l^2}$  

This is an inverse variation. Choose two other points that make this a complete inverse variation.

{(3, 15), ( , ), ( , )}

• (3, 6)

• (1, 5)

• (5, 9)

• (1, 45)

The Height of a wave in California varies directly with the seconds that pass by. At 4 seconds, the wave is 6 feet high. How many seconds will give you a wave that is 10 feet high?

• $\frac{2}{3}$

• 6

• $\frac{20}{3}$

• 7

y varies directly as the square of x and indirectly with z. If y is 8 when x is 4 and z is 6, find y when x is 8 and z is 4.

• 3
• 12
• 48
• 64

If y varies directly with x and y = 15 when x = 12 find y when x = 32.

• 40

• -40

• 5

• -5

The electrical resistance of a wire varies directly as its length and inversely as the square of its diameter. If the resistance of 640 feet of copper wire 1/4​ inch in diameter is 16 ohms, find the resistance of 320 feet of the same type of copper 1/2 inch in diameter.

If the speed of a car varies directly as the distance it travels, and the car is traveling at 60 km/h when it has traveled 150 km, what is the speed of the car when it has traveled 300 km?

• 120 km/h

• 80 km/h

• 90 km/h

• 100 km/h

Write the equation for the table given.

• $y=\frac{1}{3}x$

• $y=\frac{48}{x}$

• $y=3x$

• $y=\frac{3}{x}$

If y varies directly with x and y = 5 when x = 7, what is the constant of variation?