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Consider 12 face diagonal of a cubical block . How many pairs of them are skew lines .

I thought about it a lot . But don't get any idea . Can anybody help me in this .

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1 Answer

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Draw a picture and note that each diagonal has 5 skew lines to make pairs with.

So, 12 * 5 = 60. However, we have counted each pair twice. So, divide by two to get your answer: 30

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