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

 
wiskdls  Apr 15, 2018
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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

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