Suppose 4 digits 2 ,4,6 and 9 are given.
You have to make a four-digit number.
In how many ways it can be done, if repetition of the numbers does not allowed?
A man has 53 socks in his drawer. They are 21 identical blue, 15 identical black and 17 identical red. The light went off and he is in complete darkness. How many socks must he take out to be 100% certain that he has a pair of black socks?
How many ways can we arrange the numbers 1 through 9 in a 3x3 grid such that the following conditions hold?
- Every number is greater than the number directly above it.
- Every number is greater than the number immediately to the left of it.