If N varies directly as M and N 8 when M 20 fin... - WAEC Mathematics 2001 Question
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 option: c
N ∝ M
∴N = kM where k is a constant
N = 8 when M = 20
∴ 8 = k x 20
\(k = \frac{8}{20} = \frac{2}{5}\
∴ N = \frac{2}{5}M\
If N = 7\
∴ 7 = \frac{2}{5}M\
M = \frac{35}{2} = 17\frac{1}{2}\)
∴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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