PSAT Math › How to find the perimeter of an acute / obtuse isosceles triangle
Two sides of an isosceles triangle are 20 and 30. What is the difference of the largest and the smallest possible perimeters?
The answer cannot be determined
0
30
15
10
The trick here is that we don't know which is the repeated side. Our possible triangles are therefore 20 + 20 + 30 = 70 or 30 + 30 + 20 = 80. The difference is therefore 80 – 70 or 10.