Question

18 people were poled and 10 said they have shopped at Wal-Mart and 8 said they have shopped at Target. 4 said they shopped at both. What is the probability that the group shopped at Wal-Mart or Target?.

Answer 1

We know that 4 people shopped at both, so if we subtract 4 from the people who shopped at Walmart and Target, we get the number of people who shopped only at Walmart and Target.

So only Walmart = 10 - 4 = 6
Only Target = 8 - 4 = 4
So we're left with 4 people who didn't shop at either.
So the probability of someone in the group shopping at either only Walmart or Target is:
# of only Target) + # of only WalMart/
total #

which is:
(6+4)/18 = 10/18