Sam and two friends put letters in envelopes on Monday. The three of them take two hours to put 600 letters in envelopes.
On Tuesday Sam has three friends helping.
Working at the same rate, how many letters should the four of them be able to put in
envelopes in two hours?

Aclassroom is made up of 11 boys and 14 girls. the teacher has four main classroom responsibilities that she wants to hand out to four different students (one for each of the four students). if the teacher chooses 4 of the students at random, then what is the probability that the four students chosen to complete the responsibilities will be all boys?