A can do a work in 15 days and B can do it in 10 days. If they work together for 4 days, then the fraction of the work that is left is:

$\frac{3}{4}$ $\frac{2}{3}$ $\frac{1}{3}$ $\frac{1}{4}$

$\frac{1}{3}$

A = 15 days, B = 10 days, ⇒ A + B worked for 4 days = (2 + 3) x 4 = 5 x 4 = 20 units, ⇒ Remaining work = 30 - 20 = 10 units, ⇒ Fraction of work left = \(\frac{10}{30}\) = \(\frac{1}{3}\)