Question

in an entrance test 22 questions are set. In how many ways can you choose 18 questions to answer?​

Answer 1

Answer:

Simply, either you choose 8 questions out of 10 to answer or 2 questions out of 10 not to answer. The answer is same and it is 10C2. And this is solved as 10!/(8!×2!). The answer is 45. Always when you get a question to select r things for n things, the answer is nPr. Which is again n!/{r!×(n-r)!}.