a can do a piece of work in 14 days which b..., Time & Work, General Mathematics

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Question:A can do a piece of work in 14 days which B can do in 21 days. They begin together but 3 days before the completion of the work, A leaves  off. The total number of days to complete the work is :

A  $6 3/5$  
B  $8 1/2$  
C  $10 1/5$  
D  $13 1/2$

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+ AnswerC

+ Explanationsolution:
B's 3 day's  work = $(1/21 xx 3)$ 
                            =  $1/7$ .
Remaining work = $(1 - 1/7)$ 
                          =  $6/7$ 
 $(A + B)$ 's 1 day's work =  $(1/14 + 1/21)$ 
                                       = $5/42$ .
Now,  $5/42$  work is done by A & B in 1 day.
 $:. 6/7$  work in done by A &  B in  $(42/5 xx 6/7)$ 
                                                      = $36/5$  days.
 $:.$  Total time taken =  $(3 + 36/5)$  days 
                                 =  $10 1/5$  days.

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Question:A can do a piece of work in 14 days which B can do in 21 days. They begin together but 3 days before the completion of the work, A leaves off. The total number of days to complete the work is :

A 6356 3/5

B 8128 1/2

C 101510 1/5

D 131213 1/2

C

A $6 3/5$

B $8 1/2$

C $10 1/5$

D $13 1/2$