One angle of a quadrilateral has a measure a°. Find the average of a measures of the other three angles.

a + sum = 360

sum = (360 -a)
average = sum/3 = (360-a)/3 or 120 - a/3

The sum of the angles in a quadrilateral is always 360 degrees. Since one angle has a measure of a degrees, the sum of the other three angles is 360 - a degrees.

To find the average of these three angles, we divide the sum by 3:

Average = (360 - a) / 3

Therefore, the average of the measures of the other three angles is (360 - a) / 3 degrees.

To find the average of the measures of the other three angles in a quadrilateral, we need to consider that the sum of all the angles in a quadrilateral is always equal to 360 degrees.

Let's denote the measures of the other three angles as x, y, and z. We know that a + x + y + z = 360 degrees.

We need to find the average, which is the sum of the measures of the three angles divided by 3:

Average = (x + y + z) / 3

To solve for the average, we need to express the equation in terms of a single variable.

Rearranging the equation, we have:
x + y + z = 360 - a

Substituting this expression for the sum into the equation for the average, we get:
Average = (360 - a) / 3

Therefore, the average of the measures of the other three angles in the quadrilateral is (360 - a) / 3 degrees.