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Kritisood
An unbiased coin (a coin which has an equal probability of heads and tails) is tossed 4 times, what is the probability that it shows three same results out of the 4 times?

A. 1/6
B. 1/8
C. 1/4
D. 1/2
E. 3/4

Solution:

The probability of getting 3 tails and 1 head is ½ x ½ x ½ x ½ x 4!/3! = 1/16 x 4 = ¼. Likewise, the probability of getting 3 heads and 1 tail is also ¼. Therefore, the probability of getting 3 same results out of the 4 times is ¼ + ¼ = ½.

Answer: D
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Kritisood
An unbiased coin (a coin which has an equal probability of heads and tails) is tossed 4 times, what is the probability that it shows three same results out of the 4 times?

A. 1/6
B. 1/8
C. 1/4
D. 1/2
E. 3/4

Searched the forum for a similar ques before posting
To me the simplest way is:

total possibilities = 2^4 = 16

Favorable outcomes will be either the combinations of HHHT or THHH and we just need to see how we can order these two possibilities.

Ordering 4 items with 3 repeats = 4! / 3! = 4

since we have two possible combinations (H reapeated or T repeated) we need to multiply by 2.

Probability = (2*4)/16 = 1/2

IMO D
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