Year 9 Proportion

Question 1

y is directly proportional to x

Answer 1

y ∝ x
y = kx
k is the proportion

Question 2

y is inversely / indirectly proportional to x

Answer 2

y ∝ 1 / x
y = k / x
k is the proportion

Question 3

a is directly proportional to b, a is 20 when b is 4
What is a when b is 6

Answer 3

a ∝ b so a = kb
20 = k4
k = 5

a = 5 x 6
a = 30

Question 4

a is inversely proportional to b, a is 3 when b is 18
What is a when b is 6

Answer 4

a ∝ 1 / b so a = k / b
3 = k / 18
k = 3 x 18 = 54

a = 54 / 6
a = 9