Question

If y varies directly as x , and y = 6 when x = 15, find y when x = 25

Answer 1

y = 10

Explanation:

Given that y varies directly as x then the equation relating them is

y = kx ← k is the constant of variation

To find k use the condition y = 6 when x = 15, thus

6 = 15k ( divide both sides by 15 )

k =
`(6)/(15)` =
`(2)/(5)`

y =
`(2)/(5)` x ← equation of variation

When x = 25, then

y =
`(2)/(5)` × 25 = 10

Answer 2

10

Explanation:

let y=kx, k is constant

when y=6, x=15

6=k x 15

k=0.4

when x=25,

y= 0.4 x 25

y=10