Question

A and b can together finish a work in 30 days. They worked together for 20 days and then b left. After another 20 days, a finished the remaining work. In how many days a alone can finish the job?



a.40



b.50

Answer 1

A and B can together finish a work in 30 days.they worked together for 20 days and then B left . After another 20 days , a finished the remaining work . in how many days A alone can finish the job ?

(A + B )'s 30 days work = 1/ 30 units

since they worked together for 20 days .then Find the work done by A and B in 20 days.

( A + B )'s 20 days' work = ( 1 × 20 )/ 30

= 20 / 30 = 2 / 3 units

Find the remaining work :
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remaining work = 1 - ( 2/ 3) = 1 / 3 units

since , B left the work after 20 days , so it means that the remaining work is done byA alone. in given statement it is also mentioned that A finished the remaining work in 20 days.

since , remaining work = 1/ 3 units

1/3 units work is done by A in 20 days.

then,

whole work will be done by A in

( 20 × 3 ) = 60 days

therefore,

A alone can finish the job in 60 days .

Answer : 60 days (none of the above)

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Answer 2

Amount of work A and B do the work in 30 days

⇒ 1 day = 1/30 of the work

⇒ 20 days = 20 x 1/30 = 20/30 = 2/3 of the work

Find the remaining of the work:

Remaining of the work = 1 - 2/3 = 1/3

A can finish the remaining of the work in 20 days:

1/3 of the work = 20 days

3/3 of the work = 20 x 3 = 60 days

Answer: A can finish the work alone in 60 days