Kaplan Page 136 #19

If 3 coins are tossed simultaneously, what is the probability of getting exactly 2 tails?

The answer is 3/8. Instead of listing all the cases, is there a faster way to solve this problem?

Thanks in advance

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- Dec 4th 2008, 04:48 PMfabxx[SOLVED] coin probability problem
Kaplan Page 136 #19

If 3 coins are tossed simultaneously, what is the probability of getting exactly 2 tails?

The answer is 3/8. Instead of listing all the cases, is there a faster way to solve this problem?

Thanks in advance - Dec 4th 2008, 05:20 PMnzmathman
Every coin flip has a $\displaystyle \frac{1}{2}$ chance of turning up heads or tails.

You can have T, T, H or T, H, T or H, T, T

Each of these 3 outcomes has a probability of $\displaystyle \frac{1}{2} \times \frac{1}{2} \times \frac{1}{2} $

So probability for exactly 2 tails for 3 coin tosses = $\displaystyle 3 \left( \frac{1}{2} \right)^3 = \frac{3}{8}$