The arithmetic mean of the other two numbers is 7.2. One number is 1.6. Find the second number.

In order to find the second number, we need to draw up an equation in which we denote the unknown number by x. Let’s make the following equation:
(x + 1.6) / 2 = 7.2.
x + 1.6 = 7.2 * 2.
x + 1.6 = 14.4.
x = 14.4 – 1.6.
x = 12.8 is the second number.
Checking.
(12.8 + 1.6) / 2 = 14.4 / 2 = 7.2.
7.2 = 7.2.
The equation was solved correctly, since its right side is equal to its left side.
Answer. The second unknown number is 12.8.