4 Boys and 3 girls are standing in a straight line. Find the probability that girls and boys stand alternatively. Please answer as soon as possible.
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Solution
P(BGBGBGB)=47×36×35×24×23×12×11=4!3!7!=(3×2)(7×6×5)=135 That's because at first there are 4 boys out of 7 children. Then there are 6 children left and 3 are girls so the next probability is 36, and so on.