18 mice were placed int wo experimental groups and one control group, with all groups equally large. In how many ways can the mice be placed into three groups?

In how many ways can 5 sportsmen be selected from a group of 10 ?

A group consists of 4 girls and 7 boys. In how many ways can a team of 5 members be selected if the team has: no girl.

A group consists of 4 girls and 7 boys. In how many ways can a team of 5 members be selected if the team has: at least 3 girls.

A person writes letters to six friends and addresses the corresponding envelopes. In how many ways can the letters be placed in the envelopes so that all of them are in a wrong envelope

How many groups are there in d-block element?

Why do you think the noble gases are placed in a separate group?

In how many ways can 15 things be divided into groups of 8, 4 and 3 respectively.