If Ben and David work together, they can complete a job in 10 days. If Ben and David worked together for 5 days, followed by David who worked alone for the next 15 days, they can finish off the job.
- How many days would David need to complete the job alone?
- How many days would Ben need to complete the job alone?
(a)
Time taken by Ben and David if they work together:
10 days → 1 job
1 day →
110 job
5 days →
510 =
12 job
Time taken by David if he works alone:
15 days → 1 -
12 =
12 job
1 day →
12 ÷ 15 =
12 x
115 =
130 job
1 job → 30 days
(b)
Time taken by Ben if he works alone:
1 day →
110 -
130 =
230 =
115 job
115 job → 1 day
1 job → 1 ÷
115 = 15 days
Answer(s): (a) 30; (b) 15