direct and inverse variation

y varies directly with x. If y= -5 when x= -3 , find the equation that relates x and y and the value of y when x=12.

• y= -3/5x; -7.2
• y= -5/3x; -20
• y= 3/5x; 7.2 
• y= 5/3x; 20

Which equation shows direct variation?

• y= 5/x
• z= 5xy
• y= 5x
• 5y=x

y varies directly with x. If y= 8 when x= 4 , find the equation that relates x and y and the value of y when x=12.

• y=2x; 24
• y=4x; 48
• y=1/2x; 6
• y=32x; 384

 Y varies inversely with x, and y is 0.5 when x is 4. Which equation represents this situation?

• y=2x
• y=2/x
• y=4x
• y=x/2

Suppose y varies directly with x.
If  y = 22.5 when x = 15, find y when x = 20.

• 1.5
• 337.5
• 30
• 16.875

Suppose y varies inversely with x.
If y = 150 when x = 2, find y when x = 25.

• 300
• 75
• 1,875
• 12

y varies inversely with x. If y= 9 when x= 1 , find the equation that relates x and y and the value of y when x=3

• y=9x; 27
• y=9/x; 3
• y= x/9; 1/3
• y=3/x; 1

z varies jointly with x and y. If y= -6, x= 2, and z=24 , find the equation that relates x, y, and z.

• z=-3xy
• z= 3xy
• z= 2xy
• z= -2xy

z varies jointly with x and y. If y= 6, x= 8, and z=12 , find the equation that relates x, y, and z. Then find z when x= -4 and y= 5

• z=4xy; -80
• z=1/4xy; -5
• z= 0.25xy; 5
• z=4xy; 80

Write an equation for the given relationship:
x varies jointly with y and inversely with z

• x=ay/z
• x=az/y
• x=y/z
• x=z/y