a can do a piece of work in 80 days he..., Time & Work, General Mathematics

Question:A can do a piece of work in 80 days. He works at it for 10 days and then B alone finishes the remaining work in 42 days. The two together could complete the work in :

A 24 days 
B 25 days 
C 30 days 
D 35 days

/47

+ AnswerC

+ Explanationsolution:
Work done by A in 10 days = `(1/80 xx 10)` 
                                           = `1/8`.
Remaining work =`(1 - 1/8)`
                          = `7/8`.
Now, `7/8` work is done by B in 42 days
Whole work will be done by B in `(42 xx 8/7)`
                                                    = 48 days.
`:.` A's 1 day's work = `1/80` &
      B's 1 day's work = `1/48`.
`:. (A + B)`'s 1 day's work =`(1/80 + 1/48)`
                                        =`8/240`
                                        =`1/30`.
Hence, both will finish the work in 30 days.

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