In how many different ways can one invite 3 or more of his 6 friends?

In how many ways can one post 3 letters in 5 post boxes?

A mason has made a concrete slab. He needs it to be rectangular. In what different ways can he make sure that it is rectangular?

In how many ways can seven person be seat in a row of seats if two persons insist on sitting next to each other?

From 10 boys and 20 girls, a committee of 2 boys and 3 girls is to be formed. In how many ways can this be done if a particular boy is included

How many different teams of 11 players can be formed out of 17 players?

How many tangents can a circle have?

In how many ways can 5 prizes be awarded to 4 boys if each boy is eligible for any number of prizes?

In how many ways can the letters of the words FRACTION be arranged so that the three vowels are never together?

From 10 boys and 20 girls, a committee of 2 boys and 3 girls is to be formed. In how many ways can this be done if a particular girl is included

How many ergs make one joule?