Answer:
Explanation:
Remark
I take it you mean 5 and not 0.5.
If that is the case, this is a proportion question. A proportion consists of 4 parts. If you know 3 of the parts, you can solve for the 4th one.
Formula
Number of bags/Cost = new number of bags/Cost of the new number
Givens
original Number of bags = 5
Cost = 12.50
New number of bags = 3 bags
Cost = x
Solution
5/12.50 = 3/x Cross Multiply
5x = 12.50 * 3 Combine the right
5x = 37.5 Divide by 5
5x/5 = 37.5/5
x = 7.5
Answer: 3 bags cost 7.50 dollars.