Question

A and b can do a work in 12 days ,if b finished the work in 30 days , then how many days a takes to finish the work alone

Answer 1

$\frac{1}{a + b} - \frac{1}{b} = \frac{1}{a} \\ \frac{1}{12} - \frac{1}{30} = \frac{5 + 2}{60} \\ = \frac{7}{60} = \frac{1}{a} \\ \\ then \: a \: \frac{60}{7} = 8 \times \frac{4}{7} days$