Question

A three-character code uses the letters D and Q. Either of the letters may be repeated.

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​ Find the probability of a code with exactly two D’s.

Answer 1

1/1 x 1/2 x 1/2 = 1/4

One times One-Half times One-Half Equals One-Fourth

The Probability is 1/4 or One-Fourth.

Explanation:

There is a One-Half possibility on two of them for choosing D.

Multiply that by each other and than by 1.