Question

Twenty stamps cost 8.40. How much does it cost to buy 5 stamps

Answer 1

I think 5 stamps is ganna cost 1.68 .

Answer 2

8.40 ÷ 4 = 2.10, which is the price for those five stamps :)
5 stamps will cost $2.10
if twenty stamps cost 8.40, we want to find out how many five stamps cost.
20/5=4 
we can use this to calculate 
8.40/4=2.10, which is the price for those five stamps.