Question

Three workers have to do a certain job. The first worker can finish the job in 8 hours. The second worker can finish the job in 4 hours. The third worker can also finish the job in 4 hours. How long will it take the three workers to finish the job if they work together?
PLS help

Answer 1

Working together three workers would take 1 hour 36 minutes to finish the job

Solution:

Given that first worker can finish the job in 8 hours

So in one hour, first worker can do $\frac{1}{8}$ th of the work

The second worker can finish the job in 4 hours

So in one hour, second worker can do $\frac{1}{4}$ th of the work

The third worker can also finish the job in 4 hours

So in one hour, third worker can do $\frac{1}{4}$ th of the work

The three workers working together in 1 hour can do:

$\frac{1}{8} + \frac{1}{4} + \frac{1}{4} = \frac{1 + 2 + 2}{8} = \frac{5}{8}$

The three worker can thus do $\frac{5}{8}$ th of the work in one hour

Hence the three of them together can finish the work in $\frac{8}{5}$ hours

$\frac{8}{5} = 1\frac{3}{5}$ hours

Thus working together three workers would take 1 hour 36 minutes to finish the job