Frank can type a report in 4 hours and James takes 7 hours how long will it take the two of them typing together

Question

It's a word problem 

Answer 1

Frank can do a work in 4 hours, so his speed is 1 whole work per 4 hours, or 1/4 work per hour while James' speed is 1/7 work per hour.

 

If both are typing at the same time, just add the rates to get their speed together.

 

1/4 + 1/7 = 11/28 work per hour

 

From there, get it's reciprocal because what you need is hours per work, so the answer would be 28/11 or 2.55 hours.