Brilliant race!
Level
pending
In Brilliant race which consisting of 40 runners, 2 winners will be taken. The number of ways for runners numbered 6 and 24 to become a champion can be expressed in the abc. What is a + b?
The answer is 15.
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1 solution
Just use combinatorics theory
40C2 = \frac{40!}{38!2!} = \frac{40x39x38!}{38!2!} = \frac{40x39}{2} = \frac{1560}{2} = 780
So the equal of a+b is 7+8 = 15