Let’s assume the currency is £ (but that doesn’t really matter for the example).
Chips = £2.20
Chips + Cheese = £3.00
That means, that just the Cheese = £3.00 - £2.20 = £0.80
Chips + Beans = £2.50
That means, that just the Beans = £2.50 - £2.20 = £0.30
Chips + Cheese + Beans = £3.50
£2.20 + £0.80 + £0.30 = £3.30
I guess they did this so people don’t notice they are getting ripped off…
How did they reattach the finger to the washing machine?