Question

Y varies jointly as x and z. If y = 5 when x = 3 and z= 4, find y when x = 6 and z = 8.

Answer 1

y = 20

Explanation:

Given y varies jointly as x and z then the equation relating them is

y = kxz ← k is the constant of variation

To find k use the condition y = 5 when x = 3 and z = 4

5 = k × 3 × 4 = 12k ( divide both sides by 12 )

`(5)/(12)` = k

y =
`(5)/(12)` xz ← equation of variation

When x = 6 and z = 8 , then

y =
`(5)/(12)` × 6 × 8 =
`(5)/(12)` × 48 = 5 × 4 = 20