Answer: There are 18 houses left to be sold.
Step-by-step explanation:
If 1/3 of the houses sells, (1-1/3), or 2/3, of the houses are left. Similarly, after 5/8 of the number are sold, (1-5/8), or 3/8, are left. So the total number of houses left to be sold can be calculated as a product of these complementary fractions:
(72 new houses) x (1-1/3) x (1-5/8)=
(72 new houses) x (2/3) x (3/8) =
(72) x (1/4) = 18
There are 18 houses left to be sold.