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P does a piece of work in 15 days; Q in 20 days. If they work together for 4 days, what fraction of work is left?
A7/15
B11/15
C2/11
D8/15
Answer & Solution
Correct answer: D. 8/15
1. Per-day work: P = 1/15, Q = 1/20.
2. Combined per-day work = 1/15 + 1/20 = 4/60 + 3/60 = 7/60.
3. In 4 days combined = 28/60 = 7/15 done. Left = 1 − 7/15 = 8/15.
_Source: KMAT Karnataka 2021 PYQ Q.32_