Question

Question #f5a07

Answer 1

First, we must find out how much of the job remains and then how long the two will need.

Explanation:

The first sec. worked for 2 hours and so completed a fraction `2/8=1/4` of the job, leaving `3/4` of the job to do.
If they now both work for `x` hours, the first will complete `x/8` of the job and the second `x/10`.
So we need to solve `3/4=x/8+x/10`.

Multiplying both sides by 40 gives `30=5x+4x=9x`.
And so `x=10/3` hours or 3 hours and 20 minutes.