Question

78. A father can do job as fast as his 2 sons
working together. If one son does the job in
3 hours and the other son to 6 hours, how many
hours does it take the father to do the job​

Answer 1

one hour

remember that, father does the work x hour.one son finish 1÷6work at one hour.other son finish 1÷3 work at one hour.they work 1÷2 part of whole work together.on other side, father does 1÷x work at one hour.

so, 1÷x=1÷2

so that x=2

so that father does the work at 2 hour