Question

A and b together can complete a work in 12 days. A alone can complete it in 20 days. If b does the work only for half a day daily, then in how many days a and b together will complete the work? 10 days

Answer 1

A and B → 15 days

A → 20days

So, let's take LCM of 15 and 20. That's 60.

Remember: This 60 unit is the total work to be done.

So, A and B do (60/15) = 4 unit work/day …(1)

And, A does (60/20) = 3 unit work/day …(2)

(1)-(2) gives

B does (4–3)= 1 unit/day

So, Total days req. = (Total work)/unit per day

i.e, B can do it in (60/1)=60 days.

Answer 2

Work done by A in 1 day  

=1/20  

Work done by A and B in 1 day  

=1/12  

Therefore, Work done by B in 1 day  

=1/12−1/20

=1/30

Work done by B in half a day  

=1/60

therefore, A's 1 day work + B's half day work  

=1/20+1/60

=1/15

15 days will a and b need to work together will complete the work in 10 days