1. Show solution andillustration.

A box contains 3 white balls and 3 black balls. If they are drawn out at random, one at a time, what is the probability that they will be alternately white and black until the box is empty.

Ans: 1/20

2. Show solution and illustration.

Six draws are made from an ordinary deck of playing cards, the card drawn being replaced and the deck thoroughly shuffled before the next draw is made. What is the probability of obtaining exactly 4 spades?

Ans: 135/4096