To promote the launch of a new Cradbury's chocolate bar they are offering a, "buy four, get one free" deal. If each chocolate bar costs thirty pence, how much would ten chocolate bars cost?
If we get five for the price of four, ten will cost the same as eight. Hence ten chocolate bars will cost 8 0.30 = £2.40.
How much would seventeen chocolate bars cost?
What if you wanted to buy n chocolate bars?
What if it they offered a, "buy three, get one free" deal?
Can you generalise?