Shopping for groceries with children is a great context for estimation. Start with having everyone estimate the bill before the register shows the total. It’s amazing how much mental math is involved with figuring out whose prediction is closest.
For example, if one person has guessed the bill to be $102.54 and another person has guessed 104.13, which one is closer to the final bill of $103.34? Find the differences by subtraction.
103.34-102.54 = .80, but 104.13-103.34 = .79. So the person who predicted $104.13 would be closest.
A child can also figure the change before the cashier returns it.
Play “Beat the Calculator”
Another way to bring in estimation is to work directly from the receipt, without showing the total. Have the child estimate the total within $1.00 before someone else finds the total on a calculator. Discuss strategies for efficient estimation such as combining the cents into 5’s and 10’s.
The game, “Beat the Calculator”, can be found in the curriculum, Investigations in Number, Data, & Space (2006), Money, Miles, & Large Numbers Curriculum Unit, p. 70. Dale Seymour Publications. Many lessons and homework assignments in this curriculum are in a similar game format and can often be completed with materials typically found at home.