The correct answer is (b) 0.40.
To find the average number of units of work completed per minute, we first need to find the total number of units of work completed by all five people. We can do this by multiplying the number of units of work each person can complete per minute by the number of minutes it takes them to complete the work:
- A can complete 1 unit of work per minute in 4 minutes, so they complete 4 units of work in total.
- B can complete 0.8 units of work per minute in 5 minutes, so they complete 4 units of work in total.
- C can complete 0.667 units of work per minute in 6 minutes, so they complete 3.99 units of work in total.
- D can complete 0.4 units of work per minute in 10 minutes, so they complete 4 units of work in total.
- E can complete 0.333 units of work per minute in 12 minutes, so they complete 3 units of work in total.
The total number of units of work completed by all five people is 16.
The average number of units of work completed per minute is 16 / 5 = 0.40.
Option (a) is incorrect because it is the number of units of work completed by A per minute. Option (c) is incorrect because it is the number of units of work completed by B per minute. Option (d) is incorrect because it is not a valid answer choice.