Ten coins are tossed simultaneously. In how many of the outcomes will the third coin turn up a head?

There are 2 brothers among a group of 20 persons. In how many ways can the group be arranged around a circle so that the…

In a certain laboratory, chemicals are identified by a colour-coding system. There are 20 different chemicals. Each one …

In an examination paper, there are two groups each containing 4 questions. A candidate is required to attempt 5 question…

In how many different ways can letters of the word OFFICES be arranged?

How many integers, greater than 999 but not greater than 4000, can be formed with the digits 0, 1, 2, 3 and 4 if repetit…

From a group of 7 men and 6 women, five persons are to be selected to form a committee so that at least 3 men are there …

How many ways can 10 letters be posted in 5 post boxes, if each of the post boxes can take more than 10 letters?