if y varies directly as x and y 9 when x30 find y when x40So

if y varies directly as x, and y =9 when x=30, find y when x=40

Solution

y varies directly as x.

So, y = kx, ... (1)

where \'k\' is proportionality constant.

It is given that y=9 and x=30.

Substitute these values in (1),

9 = 30 k

Divide both sides by 30,

k = 9/30 = 3/10

Substitute this in (1),

y = 3/10 (x)

Substitute x=40

y = 3/10 (40) = 12

So the answer is y=12.