Question 306566
I man can paint a house in 6 days and his son in 12 days.
 How many days will it take them if they painted it together?
:
Let t = time required when doing the job together
:
Let the completed job = 1
:
Each will do a fraction of the job, the two fractions add up to 1
:
{{{t/6}}} + {{{t/12}}} = 1
multiply by 12 to clear the denominators, results:
2t + t = 12
3t = 12
t = {{{12/3}}}
t = 4 days together
;
:
Check it
4/6 + 4/12 = 1