Question

A person A, B and C completed one work in 8 day's. only B completed same work in 20 days.C completed same work in 30 days. then how many days will A be completed same work? ​

Answer 1

$a + b + c = 8 \\ \frac{1}{a} + \frac{1}{b} + \frac{1}{c} = \frac{1}{8} \\ \frac{1}{a} + \frac{1}{20} + \frac{1}{30} = \frac{1}{8} \\ \frac{1}{a} = \frac{6 + 4 + 15}{120} = \frac{25}{120} \\ a = \frac{120}{25} = 4.8 \: days$