Question

Two of the three sides of a triangle are 20 and 15. Which of the following numbers is not a possible perimeter of the triangle?

Answer 1

e. 72.

Let x be the measurement of the 3rd side.

x should be greater that the difference of 2 sides
x should be less than the sum of 2 sides

20 - 15 < x < 20 + 15
5 < x < 35

We can assume that x = 35 the maximum measurement of the 3rd side.

Perimeter = 20 + 15 + 35 = 70. Maximum perimeter.

Among the choices, 72 is beyond the maximum, so it is not a possible perimeter of the triangle.