Question

If a and b are inversely proportional , a=9 when b = 8 , find b when a =12.

Answer 1

Answer:

A is inversely proportional to the cube of B

⇒ A = k/B³ where k is a constant

Find k:

When A = 3, B = 2

3 = k/2³

k = 3 x 2³

k = 24

Therefore the equation is A = 24/B³

Find the value of B when A = 8/9 :

A = 24/B³

8/9 = 24/B³

8B³ = 24 x 9

8B³ = 216

B³ = 216 ÷ 8

B³ = 27

B = ∛27

B = 3

Answer: The value of B is 3.

Answer 2

Ello

A is inversely proportional to the cube of B

⇒ A = k/B³ where k is a constant

Find k:

When A = 3, B = 2

3 = k/2³

k = 3 x 2³

k = 24

Therefore the equation is A = 24/B³

Find the value of B when A = 8/9 :

A = 24/B³

8/9 = 24/B³

8B³ = 24 x 9

8B³ = 216

B³ = 216 ÷ 8

B³ = 27

B = ∛27

B = 3

Answer: The value of B is 3.

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