Five packs of pencils and three notebooks cost $23.00. Five packs of pencils and one notebook cost $20. Estimate the cost of one pack of pencils to the nearest dollar. If your child figures out that the notebooks cost $1.50 each and $20 minus $1.50 (for the remaining notebook) is $18.50, it's easy to estimate a price of about $4.00 ($3.70 to be exact).