**18. Correct. The answer is
false.**

10%, 25%, and 75% are percentiles of the income distribution. First, we
have to obtain the distribution function from the density in problem 16:

_{}

The 10%-ile is the value of 'a' for which P (X ≤ a) = 10%.
The solution is (18a^{2}-a^{4})/81 = 0.1. Using the solution
method of problem 16, we have that a ≈ 0.68 (US$ 680).

The 25%-ile is the value of 'a' such
that (18a^{2}-a^{4})/81 = 0.25, and you can find a ≈
1.098 (US$ 1098).

The 75%-ile is the value of 'a'
such that (18a^{2}-a^{4})/81 = 0.75, and you can find a ≈
2.121 (US$ 2121).