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A and B complete a work in 6 days. If A alone can do it in 7 days, then B alone can do it in ______________ days.
Question

A and B complete a work in 6 days. If A alone can do it in 7 days, then B alone can do it in ______________ days.

A.

44

B.

42

C.

43

D.

41

Correct option is B

Given:

A and B together can complete the work in 6 days.
A alone can complete the work in 7 days. 

Solution: 

Total work = LCM of 6 and 7 = 42 

Efficiency of A and B = 426\frac{42}{6}   = 7 unit/day 

Efficiency of A = 427\frac{42}{7}  = 6 unit/day  

Efficiency of B = 7 - 6 = 1 unit/day 

B will complete the whole work = 421=42\frac{42}{1} = 42  days ​

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