This is the concept of proportionality, we are required to calculate for the number of hours two crews can use to paint the house altogether. Here proceed as follows; number of hours new crew can paint=12 hrs portion of work painted by new crew in 1 hour= 1/12
number of hours experienced crew can paint=6 hours Portion of work painted by experienced crew in 1 hour=1/6
Portion of work painted by the two crews altogether in 1 hour will be: 1/6+1/12=1/4
thus the total amount of hours that the two painters will take to paint will be: 4 hours
