Question

A man, woman and a child can do a work in 3 ,4 and 12 days respectively. how many boys must assist 1 man and 1 women so as to finish the work in 1 day

Answer 1

One man's 1 day's work = 13
One woman's 1 day's work = 14
One boy's 1 day's work = 112
(1 man + 1 woman) 1 day's work
= 13+14=712
Remaining work = 1 - 712=512
Now, 112 work in done by = 1 boy 512 work is done by 
= 1*512112 
= 121 x 512=5
Hence, 5 boys shpuld assist one man and one woman to finish the work

Answer 2

man can work in 3 days
women can work in 4 days
child can work in 12 days
man and women can do the work in one day=
=1/3+1/4
=7/12
ie 12/7 days

if child also added work done in one day by three =7/12+1/12
=8/12
ie remaining work=1-8/12=4/12
=4(1/12)
=4 boys extra added after one boy already added
I.e total 5 boys are added