If N varies directly as M and N = 8 when M = 20 find
MATHEMATICS
WAEC 2001
If N varies directly as M and N = 8 when M = 20 find M when N = 7
- A. 13
- B. 15
- C. \(17\frac{1}{2}\)
- D. \(18\frac{1}{2}\)
Correct Answer: C. \(17\frac{1}{2}\)
Explanation
N ∝ M
?N = kM where k is a constant
N = 8 when M = 20
? 8 = k x 20
\(k = \frac{8}{20} = \frac{2}{5}\\
? N = \frac{2}{5}M\\
If N = 7\\
? 7 = \frac{2}{5}M\\
M = \frac{35}{2} = 17\frac{1}{2}\)
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