Question

Given that y is directly proportional tox, and when y = 8 when x=

10.
(a) Write down the equation of y in terms of x.
(b) Find the value of y when x = 25.
8
(c) Find the value of x when y==
25

Answer 1

see explanation

Explanation:

(a)

Given that y is directly proportional to x then the equation relating them is

y = kx ← k is the constant of proportion

To find k use the condition y = 8 when x = 10. then

8 = 10k ( divide both sides by 10 )

0.8 = k

y = 0.8k ← equation of proportion

(b)

when x = 25, then

y = 0.8 × 25 = 20

(c)

when y = 25, then

25 = 0.8x ( divide both sides by 0.8 )

x = 31.25