Question

A bag contains 5 pieces of string. The lengths of the pieces of string are 1 inch, 3 inches, 5 inches, 7 inches, and 9 inches. Suppose you pick three pieces of string from the bag at random and all pieces are equally likely to be chosen. What is the probability you can form a triangle with the three pieces

Answer 1

30%

Explanation:

There are 10 possible combinations of sticks that can be drawn from a group of 5 strings

5C3 = (5*4*3)/(3*2) = 10 combinations, which are

1,3,5 ; 1,3,7 ; 1,3,9 ; 1,5,7 ; 1,5,9 ; 1,7,9 ; 3,5,7 ; 3,5,9 ; 3,7,9 ; 5,7,9

to make a triangle, the sum of any two sides must be greater than the third side and if you look at the possible combinations there are only three cases where that is true

so the probability for drawing three sticks that would make a triangle is 3/10 or 30%