TV Channel Survey

A survey was taken among 100 people to find their preference of watching T. V. programs. There are 3 channels. Given the number of people who watch
� At least channel 1
� At least channel 2
� At least channel 3
� No channels at all
� At least channels 1and 3
� At least channels 1 and 2
� At least channels 2 and 3
Find the number of people who watched all three.