Question 479128
it takes Bert an hour to do a job that Harry can do in 40 minutes. one morning they worked together for 12 minutes; then Bert went away and Harry finished the job. How long did it take him to finish?
**
Bert can do the job in 60 minutes,
so, his work rate=1/60
Harry can do the job in 40 minutes,
so, his work rate=1/40
Sum of individual work rates=work rate when working together
1/60+1/40=1/x
(40+60)/2400=1/x
100/2400=1/x
x=24
work rate when Bert and Harry work together=1/24
If they worked for 12 minutes, the would have completed 12*1/24 =12/24=1/2 of the job.
Since Harry can do the entire job alone in 40 minutes, he will need only 20 minutes to finish half of the job.
ans:
Harry took 20 minutes to finish the job.