If N varies directly as M and N = 8 when M = 20 find…

If N varies directly as M and N = 8 when M = 20 find M when N = 7

Correct Answer: Option C

Explanation

N ∝ M
∴N = kM where k is a constant
N = 8 when M = 20
∴ 8 = k x 20
(k = frac{8}{20} = frac{2}{5}\
∴ N = frac{2}{5}M\
If N = 7\
∴ 7 = frac{2}{5}M\
M = frac{35}{2} = 17frac{1}{2})