If there are 4 families in a country with a per capita income of $15000. The income of the three families is $10000, $20000 and $12000. What is the income of the 4^th family?

Per capita Income = Total income of a country / Total population

Let the income of the fourth family in the given question be $X.

$15000 = ($10000+$20000+$12000+ income of the fourth family)/4

$15000 = ($42000+x)/4

$60000 = $42000+x

X=$60000-$42000

X=$18000

The income of the fourth family = $18000.