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Why is n^k/k! not the correct number of ways to select k objects from n objects with replacement (order not important)? - Quora

Combinatorics: A frog can hop either 1 or 3 stairs at a time. In how many ways can he climb to exactly 100 stairs? - Quora

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The length of a corridor is 5.2m. Jessica walks from one end of the corridor to the other. Each step is only 0.4m or 0.8m (cannot go back). How many total ways

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How many ways are there to climb the eight-step ladder if you always step on either one or two steps at a time? - Quora

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There is a building with [math]n[/math] floors. A person can climb either 1 or 2 floors at a time. Find the number of ways to reach the nth floor? - Quora