A test consists of 20 questions, and students are asked to only answer 15 of them. In how many different ways can they choose 15 questions?

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04-11-2016
Mathematics

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A test consists of 20 questions, and students are asked to only answer 15 of them. In how many different ways can they choose 15 questions?

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HomertheGenius HomertheGenius · Answer 1 · 2016-11-05T21:03:42+01:00

HomertheGenius HomertheGenius

05-11-2016

n = 20, r = 15;
n C r = ( n * ( n - 1) ( n - 2 ) ... ( n - r + 1 )) / r ! =
20 C 15 = (20 * 19 * 18 * 17 ......8 * 7 * 6) / (15 * 14 * 13 ...* 5 * 4 * 3 * 2 * 1) =
= 15,504
Answer:
They can choose 15 questions in 15,504 ways.

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