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Passengers are to travel by a double decked bus which can accommodate 13 in the upper deck and 7 in the lower deck. The number of ways that they can be divided if 5 refuse to sit in the upper deck and 8 refuse to sit in the lower deck, is |
Answer» `20=13U+7L` Number of ways`=.^7C_5=,^7C_2` `=(7*6)/(2*1)=21`. |
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