Quadrilateral word problem help please?

Question

one angle of a quadrilateral has measure of "a" degrees. Find the average of the measures of the other three angles. It also says hint: the sum of the meaures of the angles of a quadrilateral is 360 degrees.

Answer 1

If the sum of the degree measures of the angles of a quadrilateral is 360°, then the three remaining angles sum to (360° - a), where "a" is the measure of the known angle.  Their average, Avg = (360° - a)/3 = 120° - a/3.  They won't necessarily average to 90°.  Suppose one of the angles has a degree measure of 135°.  Then the remaining 3 angles sum to 360° - 135° = 225°, and their average is 225°/3 = 75°, which obviously is not 90°.

Notice, using our example and the equation for the average above, if a = 135°, then Avg = 120° - (135°/3) = 120° - 45° = 75°, which is what we also obtained above.

So the best way to answer this question is this:

Avg = 120° - a/3.

Answer 2

90 degrees because since 360 is the whole degrees of a quadrilateral, you divide 360 by the 4 sides of the square...

360/4=90 degrees