Question 773527
Mr B does the job in 1/15 job per minute
His Son can do the job in 1/30 job per minute.
Together rate = 1/x job/min
1/15 + 1/30 = 1/x
Common Denominator = 30x
2x + x = 30
3x = 30
x = 10
So, together they can do the 
job in 10 minutes.
Hope this helps.
:-)