Question

If y varies directly with x, and y = 2 when x = −4, what is the value of y when x = 20 ?

Answer 1

y = - 10

Explanation:

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

y = kx ← k is the constant of variation

To find k use the condition y = 2 when x = - 4, that is

2 = - 4k ( divide both sides by - 4 )

`(2)/(-4)` = k, that is

k = -
`(1)/(2)`

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

When x = 20, then

y = -
`(1)/(2)` × 20 = - 10

Answer 2

y=kx

2=k.-4

k=-1/2

then

y=-1/2×20

y=-10