Time and Work Practice Test 4 with solutions

Work done by one man in one day = $\frac{1}{4}$
Work done by 2 men in one day = $\frac{1}{2}$
Work done by 2 women in one day = $\frac{2}{5}$
Work done by 2 men and 2 women in one day
= $\frac{1}{2}+\frac{2}{5}$ = $\frac{9}{10}$
Remaining work = $\frac{1}{10}$
Work done by one boy in one day = $\frac{1}{10}$
So, they need to be assisted by one boy.