Question

Jay was reaching into her purse and accidentally spilled her coin purse. 10 pennies fell on the floor. Jay noticed that only 2 of the pennies landed on heads. What is the theoretical probability of this happening?

Answer 1

4.39%

Explanation:

There are no marking to identify the coins, so the order is not important. Since the order not important we use combination instead of permutation.

A coin have 2 possible outcome, head or tails. Assuming the coin is fair each outcome will be 50% or 0.5 chance. If heads= A and tails =B, then the probability of 2 pennies will be:

P(A=2) = 2C10 * A^2 * B^(10-2)

P(A=2) = 10*9/2 * 0.5^2 * 0.5^8

P(A=2) = 0.0439= 4.39%