How to Estimate Quantities Using Benchmarks

Instructor: Mark Boster
Sometimes you will be asked to estimate quantities, such as how much lasagna is left over from dinner. In this lesson, you will learn how to estimate quantities using benchmarks to describe whether something is 25%, 10%, or even almost 100% of the total.

Shopping for Milk

Bill's mother called home from the grocery store to ask if they needed more chocolate milk. She asked Bill to tell her how full the milk carton was. If it was 25% full or less, she would buy another carton. Let's find out how to estimate how full the milk carton was.

Reviewing Percentages

There are a few things to think about before we can know approximately how much milk is left in the carton. Let's try this first. Get a piece of notebook paper, the kind with lines on it and three holes on the left. If you can't find one, just get any old paper.

  1. Fold the paper in half by touching the top of the paper to the bottom, and crease it.
  2. Now, while it is still folded, touch the fold (where you creased it in step 1) to the bottom of the paper, and crease it again.
  3. Open the paper completely, and then fold the bottom of the paper up to the fold line just above the bottom, creasing it one last time.

Your paper should look like the paper in Step 3 of Diagram 1.

Diagram 1

These lines are benchmarks for you to use when estimating. A benchmark is a standard that can help you make estimates about quantities. You can compare the amount you see to these benchmarks to help you to determine if something is 10%, 25%, 50%, 75% or 100% of the total. Here are some guidelines:

  • From bottom to top, the whole paper is 100% of the paper.
  • Halfway up the paper (where you made the first crease) is 50%.
  • If you start from the bottom of the paper and go halfway to 50%, you get 25%.
  • If you go halfway between 50% and 100%, you get 75%.
  • Just below half of 25% is 10%.

Milk Cartons

Now let's try to help Bill answer his mom's question. Look at the milk cartons in Diagram 2. There are three cartons of chocolate milk. Let's estimate how much milk is in each carton.

Diagram 2

Looking at Carton A, we can see that it is about half full, or 50% full. We know this because if you could fold the carton over in half once, from top to bottom, the milk would be at about the fold line. Looking back to Diagram 1, you can see that the middle fold is 50%. It may not be full to that line exactly, but it is closest to the 50% line.

The amount of milk in Carton B looks like about half the amount of milk in Carton A. If you folded the milk in Carton A in half, the chocolate milk line would be at the fold line of the milk in Carton A, or at the 25% fold line of the whole carton. (Refer to Diagram 1 if you need to.) Carton B is 25% full.

The amount of milk in Carton C looks like less than half of the amount of milk in Carton B. Since Carton B is 25% full, we can guess that Carton C is probably about 10% full. You can always try estimating by pretending to fold the item, and comparing it to the benchmarks in Diagram 1.

Bill has Carton B in his fridge. With only 25% of the milk left, Bill's mom decided to buy another carton of chocolate milk at the store.

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