Let a, b, c, d, and e be the five positive numbers in the decreasing order of size such that e is the smallest number.
We are given that the average of the five numbers is 25. Hence, we have the equation
$\frac{\text{a}+\text{b}+\text{c}+\text{d}+\text{e}}{5}=25$
a + b + c + d + e = 125 ----------- (1) by multiplying by 5.
The smallest number in a set is at least less than the average of the numbers in the set if at least one number is different.
For example, the average of 1, 2, and 3 is 2, and the smallest number in the set 1 is less than theaverage 2. Hence, we have the inequality
0 < e < 25
0 > -e > -25 by multiplying both sides of the inequality by -1 and flipping the directions of the inequalities.Adding this inequality to equation (1) yields
0 + 125 > (a + b + c + d + e) + (-e) > 125 - 25
125 > (a + b + c + d) > 100
125 > (a + b + c + d + 0) > 100 by adding by 0
25 > $\frac{\text{a}+\text{b}+\text{c}+\text{d}+0}{5}$     ⇒ 20 by dividing the inequality by 5
25 > The average of numbers a, b, c, d and 0 > 20
Hence, x equals
(Average of the numbers a, b, c, d and e) – (Average of the numbers a, b, c, and d)
= 25 − (A number between 20 and 25)
⇒ A number less than 5
Hence, x is less than 5