The age of Mwenda is 3/5 of that of his sister.If 20 years ago the age of Mwenda was 2/5 that of his sister then. Find the present age of Mwend.

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M = 3/5 s

M - 20 = 2/5 (s - 20)

substituting ... 3/5 s - 20 = 2/5 s - 8

solve for s , then substitute back to find M