Estimation is a problem-solving strategy that is frequently used by anyone who is living on a budget. One example would be the estimated cost of a week's worth of school lunches. Let's say that the cost of school lunch for is $2.99. If we multiply that by three, the daily cost of school lunch for three children would be $8.97. If we then multiply $8.97 by five, the weekly cost of school lunch for three children would be $44.85. However, we want to avoid having to count out pennies and small change when setting aside the week's lunch money, so we instead round $2.99 to $3.00. Now the daily cost of school lunch for three children is $9.00 and the weekly cost is $45.00. By putting aside $45.00 each week, we know we have enough to cover lunch money without having to worry about miscounting the change.
Another example would be estimating how much milk to buy at the supermarket each week. Let's say that one week a family of four (a single mother and three children) uses one gallon, two quarts, and one pint of milk. We could go to the store and buy a gallon jug, a half gallon carton (two quarts), and a pint carton of milk. However, we know that a family may not use the exact same amount of milk each week and it is better to have a little left over than to run out in the middle of the week and have to spend the time and gas money to make an additional trip to the supermarket. Let's say that it is also cheaper to buy milk by the gallon than it is to buy it in smaller cartons. One gallon, two quarts, and one pint is equal to 1.625 gallons. Therefore, we would round to two gallons, ensuring that we have enough milk for the cheapest price.