The arithmetic mean of 6.4 and y is 8.5. Find the number y.

In the initial data for this task, it is reported that if we add the unknown number y to the number 6.4, and then divide the resulting sum by 2, the result will be the number 8.5, therefore, we can draw up the following equation:

(6.4 + y) / 2 = 8.5,

solving which, we get:

6.4 / 2 + y / 2 = 8.5;

3.2 + y / 2 = 8.5.

Subtracting from the parts of this ratio, standing to the left and right of the sign = number 3.2, we get:

3.2 + y / 2 – 3.2 = 8.5 – 3.2;

y / 2 = 5.3;

y = 5.3 * 2 = 10.6.

Answer: the number y is 10.6.