Mathematics
NULL
Medium
Question
A and B together finish a work in 30 days. They work 20 days, then B leaves and A finishes the rest in 20 more days. In how many days can A alone finish the work?
A
70
B
50
C
40
D
60
✓ Official correct answer
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A
70
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B
50
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C
40
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D
60
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Explanation
Together rate = 1/30. In 20 days they do 2/3; remaining 1/3 takes A 20 days ⇒ A's rate = 1/60 ⇒ A alone needs 60 days.