Question

3. Arthur can do the job in 30 min. Bonnie can do it in 40 min and Claire can do it in 60 min.
How long will it take them if they work together?

Answer 1

Artur  does 1/30 part of work in 1 min

Bonie  does  1/40 part of work in 1 min

Clarie  does 1/40 part of work in 1 min

Then together they do
$\frac{1}{30} + \frac{1}{40} + \frac{1}{60} = \frac{4 + 3 + 2}{120} = \frac{3}{40}$ part of in 1 min

Becasue all work equal 1 we will get  that they do all

work for

$1 : \dfrac{3}{40} = \dfrac{40}{3}$   min