John flips a penny, a nickel, and a dime. How many ways can she get at least two heads?

wiskdls Apr 15, 2018

#1**+2 **

Alright, here we go:

Since all we are talking about is heads or tails, what type of coin it is doesn’t matter.

There are a total of $2^3$ different outcomes when you flip three coins.

Here are all of them listed:

HHH ; HHT ; HTH ; THH ; TTT ; TTH ; THT ; HTT

Out of the eight different outcomes, only $\binom{3}{2}$ of them have 2 heads.

HHT, THH, and HTH

Since the problem is asking for at least, we can also get 3 heads, which there is only one way to do:

HHH.

There are 4 outcomes that match what the problem is asking for, so the answer is 4/8, 0.5, or 50%.

GYanggg Apr 15, 2018