nikdiablo129 wrote:
If a child flips a coin five times in a row, what is the probability that she will receive at least one head and one tail?
A) 3/4
B) 11/12
C) 15/16
D) 31/32
E) 63/64
If a coin is flipped 5 times in a row, there are
32 possible outcomes (HHTTH, HTHTT, TTTTT, etc)
How did we get
32?
Well, there are 2 possible outcomes for the 1st coin flip, 2 possible outcomes for the 2nd coin flip, 2 outcomes for the 3rd flip, 2 outcomes for the 4th flip, and 2 outcomes for the 5th flip,
By the Fundamental Counting Principle (FCP), the TOTAL number of outcomes when flipping 5 coins = (2)(2)(2)(2)(2) =
32Of course, among those
32 outcomes, there are some outcomes that DO NOT meeting the required condition that we receive
at least one head and one tailThere are EXACTLY 2 outcomes that DO NOT meet this required condition.They are: TTTTT and HHHHH
So, the number of outcomes that DO meet the required condition =
32 -
2 =
30So, P(child gets at least one head and one tail) =
30/
32= 15/16
Answer: C
Cheers,
Brent
_________________
Brent Hanneson – Creator of gmatprepnow.com
I’ve spent the last 20 years helping students overcome their difficulties with GMAT math, and the biggest thing I’ve learned is…
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