A system consists of 8 partices of different masses. How many terms appear in expression of potential energy of system?
How many different boat parties of 8, consisting of 8, consisting of 5 boys and 3 girls, can be made from 25 boys and 10 girls ?
A person wishes to make up as many different parties as he can out of 20 friends with the condition that each party consists of the same number. How many should he invite at a time?