Question

In 2012, five U.S postal stamps cost $2.20. how much did seven stamps cost? answer please

Answer 1

You'd do $2.20 and multiply it by seven. Which would give you $15.40, according to my calculations.

Answer 2

This is very easy to solve. You know that 5 stamps costs $2.20. To find out how much 1 stamp is you have to divide $2.20 by 5.   
$2.20/5=$0.44
So now we know that 1 stamp is 44 cents.
Since you want to know how much 7 stamps cost, you have to add two more stamps to the stamps you already have.
5 stamps=$2.20+ 1 stamp= $0.44 + 1 stamp= $0.44
2.20+0.44+0.44= 3.08
So, 7 stamps costs $3.08.
Get it? Let me know if you still don't understand.