A tv survey gives the following data for tv viewing, then 60% see program A, 50% see program B, 50% sees program C. 30% people see program A and B, 20% see program B and C, 30% see program A and B and 10% do not view any program. 
1) what percentage view all the 3 programs A, B and C? 
1) what percentage view exactly 2 programs