Using Inclusion-Exclusion I need to solve this Actuarial problem:
Problem 5: A Grocery store finds that:
1. 30% of its customers buy bananas
2. 22% of its customers buy soy milk
3. 45% of its customers buy cow milk
4. one third of the customers buy bananas also buy soy milk
5. one half of the customers who don't buy bananas do buy cow milk
6. none of the customers buy both soy and cow milk.
What percentage of customers don't buy bananas or milk?
This is what I have found so far is
let b = bananas
let s = soy milk
let c = cow milk
| b | = 30%
| s | = 22%
| c | = 45%
| b ∩ s | = 10%
| s ∩ c | = 0%
| b ∩ s ∩ c | = 0%
What I believe I need is |b ∩ c| which I am assuming I get from statement 5. I am unsure how to approach number five to receive what I need to complete this equation:
| b U c U s | = | b | + | c | + | s | - | b ∩ s | - | s ∩ c | - | b ∩ c | + | b ∩ s ∩ c |
then take what I get and subtract it from 100 for the percentage of customers that don't buy bananas and milk.
Am I taking the wrong approach? If not can you steer me in the proper direction for portion I am missing. Thanks