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Suppose, you are a mathematician.You went to watch a car race which you are very fond of.It was Quarter-final and race consisted of only 5 cool and different cars.In how many ways can 5 cars cross the finish line.

(ties are possible for any number of cars).


The answer is 541.

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2 solutions

Satyen Nabar
Sep 10, 2015

a) 5 cars tie - 1 way

b) 4 cars tie - 5C4 * 2! = 10 ways

c) 3 cars tie - 5C3 * 3! = 60 ways

d) 3 cars tie and a pair ties - 5C3 * 2! = 20 ways

e) 2 cars tie - 5C2 * 4! = 240 ways

f) 2 pairs of cars tie-- You can select a pair in 5C2 ways then select another pair in 3C2 ways so10*3 = 30 but there will be repeats so half that will be 15 * 3! = 90 ways

g) no cars tie -- 5! = 120 ways.

total of 541 ways

Abhijit Garg
Sep 4, 2015

Let us break 5 1+1+1+1+1 denotes all 5 racers finished at different time=5! 1+1+1+2 denotes any 2 racers finished at same time=(5C2) 4! 1+2+2 denotes any 2 pairs(2 racers at same time) finished at different time=5 3 3! 1+1+3 denotes 3 racers at same time=10 3! similarly, for 3+2----=10 2! for 4+1-----=5 2! for 5----=1 adding 'em all we get 541.

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