The question goes...

If 85% of people have a bowl of cereal for breakfast, 60% of people have some toas for breakfast, and 50% of people have both cereal and toast for breakfast, what proportion of people have neither cereal nor toast for breakfast?

I know it's simple, but I can't remember how to do it (Worried) can anyone help?

My preliminary guess (educated, obviously) was 27.5%...