Question

A and b can do a piece of work in 7 days. with the help of c they finish the work in 5 days. c alone can do that piece of work in?

Answer 1

Answer: 17.5 days

Step-by-step explanation:

Given: A and b can do a piece of work in 7 days.

With the help of c they finish the work in 5 days.

Let x be the number of days taken by c to finish the work alone, then we have the following equation:-

$\frac{1}{x}+\frac{1}{A+b}=\frac{1}{A+b+c}\\\\\Rightarrow\frac{1}{x}+\frac{1}{7}=\frac{1}{5}\\\\\Rightarrow\frac{1}{x}=\frac{1}{5}-\frac{1}{7}\\\\\Rightarrow\frac{1}{x}=\frac{7-5}{35}\\\\\Rightarrow\frac{1}{x}=\frac{2}{35}\\\\\Rightarrow\ x=\frac{35}{2}=17.5\ days$