If N varies directly as M and N = 8 when M = 20 find M when N = 7
- 13
- 15
-
\(17\frac{1}{2}\)
- \(18\frac{1}{2}\)
The correct answer is: 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 = \(\frac{2 M}{5}\)
If N = 7
∴ 7 = \(\frac{2 M}{5}\)
M = \(\frac{35}{2}\) = 17\(\frac{1}{2}\)