This is a nice weighted averages question.

Weighted average of groups combined = (group A proportion)(group A average) + (group B proportion)(group B average) + (group C proportion)(group C average) + ...

So: average age of COMBINED workers = (proportion of project managers)(average age of project managers) + (proportion of engineers)(average age of engineers)

We have a total of 24 workers (14 project managers + 10 engineers = 24 workers)
So, the proportion of project managers = 14/24 = 7/12
The proportion of engineers = 10/24 = 5/12
Let E = average age of engineers

Now, plug everything into the formula to get:
31 = (7/12)(36) + (5/12)(E)
Simplify: 31 = 21 + 5E/12
Subtract 21 from both sides: 10 = 5E/12
Multiply both sides by 12 to get: 120 = 5E
Solve: E = 24

Answer: A

RELATED VIDEO

_________________