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2007 iTest Problems/Problem 4

Revision as of 21:55, 12 December 2007 by 1=2 (talk | contribs) (→‎See Also)

Problem

Star flips a quarter four times. Find the probability that the quarter lands heads exactly twice.

$\mathrm{(A)}\,\frac{1}{8}\quad\mathrm{(B)}\,\frac{3}{16}\quad\mathrm{(C)}\,\frac{3}{8}\quad\mathrm{(D)}\,\frac{1}{2}$

Solution

The number of arrangements of the group of letters HHTT is $\frac{4!}{2!*2!}=6$, so the probability that two of the flips are heads is $\frac{6}{2^4}=\frac{3}{8} \Rightarrow D$

See Also

2007 iTest (Problems, Answer Key)
Preceded by:
Problem 3 		Followed by:
Problem 5
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