If David and Ben work together, they can complete a job in 12 days. If David and Ben worked together for 8 days, followed by Ben who worked alone for the next 20 days, they can finish off the job.
- How many days would Ben need to complete the job alone?
- How many days would David need to complete the job alone?
(a)
Time taken by David and Ben if they work together:
12 days → 1 job
1 day →
112 job
8 days →
812 =
23 job
Time taken by Ben if he works alone:
20 days → 1 -
23 =
13 job
1 day →
13 ÷ 20 =
13 x
120 =
160 job
1 job → 60 days
(b)
Time taken by David if he works alone:
1 day →
112 -
160 =
460 =
115 job
115 job → 1 day
1 job → 1 ÷
115 = 15 days
Answer(s): (a) 60; (b) 15