Question

There are n coins, each showing either heads or tails. We would like all the coins to show the same face. What is the minimum number of coins that must be reserved?

Answer 1

Answer:

Its nCr = n!/(r!.(n-r)! =n!/!!.(n-1)! = n

Explanation:

Here. the arrangement of outcome does not matters, and hence it is a combination. You should know that when arrangement matters then we have to calculate the permutation and its formula is n!/(n-r)!. However, here it is the combination, and hence its nCr or n!/r!. (n-r)!. And here r is 1 as we can have all heads or all tails. And n is n. Hence,

Its nCr = n!/(r!.(n-r)!

           =n!/!!.(n-1)!

           = n