A can do a work in 15 days and B in 20 days. If they work on it together for 4 days, then the fraction of the work that is left is :
$ \dfrac{1}{4} $
$ \dfrac{1}{10} $
$ \dfrac{7}{15} $
$ \dfrac{8}{15} $
Explanation:
As 1 days work =$ \dfrac{1}{15} $;
Bs 1 days work =$ \dfrac{1}{20} $;
$\left(A + B\right)$s 1 days work =$ \left(\dfrac{1}{15} +\dfrac{1}{20} \right) $=$ \dfrac{7}{60} $.
$\left(A + B\right)$s 4 days work =$ \left(\dfrac{7}{60} \times 4\right) $=$ \dfrac{7}{15} $.
Therefore, Remaining work =$ \left(1 -\dfrac{7}{15} \right) $=$ \dfrac{8}{15} $.