Question

The average age three people running for election is 42. A fourth person joins the race and the average drops to 40. What is the fourth person’s age?

Answer 1

Call the four people $a, b, c$ and $d$.

We know:
$\frac{a+b+c}{3}=42$

and
$\frac{a+b+c+d}{4}=40$

Thus:
$a+b+c=126$
$\frac{126+d}{4}=40$
$126+d=160$
$d=34$