Question

If Q is directly proportional to P and Q = 28 when P = 4,

(i) express Q in terms of P
(ii) find the value of Q when P = 5
(iii) Calculate the value of P when Q = 42.
Topic: Direct Proportions.

Answer 1

see explanation

Explanation:

given Q is directly proportional to P then the equation relating them is

Q = kP ← k is the constant of proportion

(i)

to find k use the condition Q = 28 when P = 4

28 = 4k ( divide both sides by 4 )

7 = k

Q = 7P ← equation of proportionality

(ii)

when P = 5 , then

Q = 7 × 5 = 35

(iii)

when Q = 42 , then

42 = 7P ( divide both sides by 7 )

6 = P