:
HHHH
HHHT
HHTH
HHTT
HTHH
HTHT
HTTH
HTTT
THHH
THHT
THTH
THTT
TTHH
TTHT
TTTH
TTTT
There are 16 ways the tosses can come out. The ways for which
there are two heads and two tails are HHTT, HTHT, HTTH, THHT,
THTH, and TTHH. Since each way has the same probablity (namely
1/2 x 1/2 x 1/2 x 1/2 = 1/16), the chance that the four tosses
result in two heads and two tails is 6/16 = 3/8 = .375, or 37.5%.
(38.29% is what you get if you use the normal curve method of
approximating the chance.)
! !I