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Earn 100
There are letters and envelopes. Find the number of ways in which only one letter goes in the wrong envelope?
50% studentsanswered this correctly
Important Questions on Permutations and Combinations
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There are four envelopes and four letters. Find the number of ways in which only two letters goes in the wrong envelopes?
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A train is running between Patna to Howrah. Seven people enter the train somewhere between Patna and Howrah. It is given that nine stops are therein between Patna and Howrah. In how many ways can the tickets be purchased if no restriction is there with respect to the number of tickets at any station? people do not buy the same ticket.
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There are seven pairs of black shoes and five pairs of white shoes. They all are put into a box and shoes are drawn one at a time. To ensure that at least one pair of black shoes are taken out, what is the number of shoes required to be drawn out?
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There are seven pairs of black shoes and five pairs of white shoes. They are all put in a box and shoes are drawn one at a time. What is the minimum number of shoes required to be drawn out to get at least one correct pair(Black or White shoes) of shoes?
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In how many ways, one white and one black rook can be placed on a chessboard so that they are never in an attacking position?
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How many -digit numbers have all their digits either all odd or all even?
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How many -digit numbers have at least even digit?
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On a triangle ABC, on the side AB, points are marked, points are marked on the side BC and points are marked on the side AC (none of the points being the vertex of the triangle). How many triangles can be made by using these points?
