Question

F is directly proportional to a.
If F = 42 when a 7 find
a when F = 18
​

Answer 1

a = 3

Explanation:

Given that F is directly proportional to a, then the equation relating them is

F = ka ← k is the constant of proportion

To find k use the condition F = 42 when a = 7, thus

42 = 7k ( divide both sides by 7 )

6 = k

F = 6a ← equation of proportion

When F = 18, then

18 = 6a ( divide both sides by 6 )

3 = a

Answer 2

a=3

Explanation:

The formula for direct proportion is

f = ka

Let f= 42 and a = 7

42 = k*7

Divide each side by 7

42/7 = k7/7

6 =k

f = 6a

Let f = 18

18 = 6a

Divide each side by 6

18/6 = 6a/6

3 =a