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You are standing on the corner of 4th Street and 4th Avenue in a city with a rectangular street system similar to New York’s (but without the exceptions). You want to meet your friend at 10th Street and 10th Avenue by walking only east and north (that is, walking the minimum possible distance). However, the corner of 7th Street and 7th Avenue is blocked due to construction and you cannot get through. How many ways are there to walk to meet your friend?

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ChoiSungHyun

Step-by-step explanation:

To get from point (4,4) to (10,10), it is the same as ordering 6 Upward and 6 Right arrows in a straight line.

=> 12C6 = 924.

However there is a restriction that we cannot have 3 Upward and 3 Right arrows as our first 6 arrows.

=> 6C3 * 6C3 = 20 * 20 = 400

Hence there are 924 - 400 = 524 different ways.

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