A can do one-third of a work in 4 days and B can do three-fourth of the work in 15 days. Together, they will complete the work in:

A4 and one-fourth days

B5 and three-fourth days

C8 and one-fourth days

D7 and one-half days ✓ Correct

Correct answer: (D) 7 and one-half days

Explanation

Together they finish in 7 and one-half days.

A does 1/3 in 4 days, so full work in 12 days, rate 1/12.

B does 3/4 in 15 days, so full work in 20 days, rate 1/20.

Combined rate = 1/12 + 1/20 = 8/60 = 2/15.

Time = 15/2 = 7 and one-half days.

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