Question

A Girl Scout is selling cookies. She currently has 3 boxes of Thin Mints, 4 boxes of Tag-Alongs, and 5 boxes of Somoas left. What is the probability that a customer will randomly buy two of the same box of cookie to purchase?

Answer 1

Probability that customer will buy 2 boxes of Thin Mints: 3/12*2/11=6/132
Probability that customer will buy 2 boxes of Tag-Alongs: 4/12*3/11=12/132
Probability that customer will buy 2 boxes of Somoas: 5/12*4/11=20/132
Thus the probability in total is 6/132+12/132+20/132=28/132=28.7879%