Explanation

(a)
Given, the probability of solving the problem are $\frac{1}{3}\ ,\frac{1}{4}\ and\frac{1}{5}$ respectively and$\$
corresponding probabilities of not solving the problem are $\frac{2}{3}\ ,\frac{3}{4}\ and\ \frac{4}{2}$ respectively
$\therefore Required\ probability = 1 - P(not\ solving\ the\ problem)$
$= 1 - \left( \frac{2}{3} \times \frac{3}{4} \times \frac{4}{5} \right)$
$= 1 - \frac{2}{5} = \frac{3}{5}$