Marketing Problem with intersection of percentages

Question

I am revising some A Level maths and I am struggling a bit with the following question...

You are a manufacturer of electronics and a marketing agency has collected the following data for you:

80% of your customers own a computer

70% own a DVD Player

and 40% own both

Should you pay the invoice from this agency?

I think the answer lies in some sort of Venn Diagram

Answer 1

It's clearly impossible that only 40% of customers own both, as 70-(100%-80%)=50% forcing a minimum 50% of customers into the overlap. The math tells you they screwed up.