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?

Perimeter of the triangle is 60.

A perimeter of a triangle can be found using the following:

1) measurement of 3 sides are given:

P = a + b + c

2) 2 sides of a right angle triangle is given:

a² + b² = c²; P = a + b + c

3) 2 sides of a triangle is given with the measurement of an angle.

c² = a² + b² - 2ab (cos (C)).

Since, only the measurement of 2 sides is given, we can assume that the triangle is a right-angled triangle.

c² = a² + b²

c² = 20² + 15²

c² = 400 + 225

c² = 625

c = √625

c = 25

P = a + b + c

P = 20 + 15 + 25

P = 60