Find the length of the third side of a triangle

Question

The lengths of two sides of a triangle are 2 and 9. Which of the following can be the length of the third side?

a)4

B)6

C)8

D)12

E)14

Answer 1

The 3rd side must be LONGER than the DIFFERENCE of the known sides, but SHORTER than the SUM of the known sides. 

Known sides measure 2 and 9

9-2 < 3rd side < 9+2

7 < 3rd side < 11

So the answer can only be 8.