Discussion :: Time and Work

A and B together can complete a task in 7 days. B alone can do it in 20 days. What part of the work was carried out by A?
I.
A completed the job alone after A and B worked together for 5 days.
II.
Part of the work done by A could have been done by B and C together in 6 days.
A.
I alone sufficient while II alone not sufficient to answer 
B.
II alone sufficient while I alone not sufficient to answer 
C.
Either I or II alone sufficient to answer 
D.
Both I and II are not sufficient to answer 
E.
Both I and II are necessary to answer 
Answer : Option A
Explanation :
B's 1 day's work =\( \frac { 1 } { 20 } \)
(A+ B)'s 1 day's work =\( \frac { 1 } {7} \)
I. (A + B)'s 5 day's work =\( \frac { 5 } {7} \)
Remaining work =[1\( \frac { 5 } {7} \)]=\( \frac { 2 } {7} \)
\( \frac { 2 } {7} \)work was carried by A
II. is irrelevant
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