Question
A frog wants to cross the pond. He saw 5 turtle’s
shell which can help him to reach at the end of pond. Frog can move either 1 or 2 steps at a time. Find the number of ways in which a frog can cross the river? (Frog can’t take double step from last shell).Solution
The frog needs to take 6 steps to cross the pond. He can do this in the following ways: Crossing the pond by 6-unit steps = 1 way. Crossing the pond by 4-unit steps and 1 double step = 5C1 = 5C4 = 5 ways. Crossing the pond by 2-unit steps and 2 double steps = 4C2 = 6 ways. Crossing the pond by 3 double steps = 1 way. Hence, the required number of ways = 1 + 5 + 6 + 1 = 13
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