Question

a can do a peace of work in 10 days but b in 12 days and c in 15 days.they all start the work

Answer 1

they all can do that work in 4 days

Answer 2

$\frac{1}{x } = \frac{1}{10} + \frac{1}{12} + \frac{1}{15}$

$\frac{11}{60} + \frac{1}{15}$
0.25