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Mental Maths – Estimating Strategy

This is the last strategy I’ll be sharing for mental maths. Some of the strategies we’ve looked at include: counting on, near doubles, compatible numbers and partitioning. I thought we’d finish with estimation as it’s quite complex and involves your students thinking about numbers in many ways.

What is estimation?

The goal of estimation is to be able to judge reasonableness. This is especially important if your students are using calculators, they should estimate an answer first, to then judge if the answer they got on the calculator is in fact reasonable. There are many different ways to estimate including rounding, finding compatible numbers, bracketing and compensating.

We can also use benchmarks when estimating. A benchmark is being able to look at a quantity and use that to estimate in different settings. For example, you might be at a football match and estimate that in one section there are 500 people. You could then use that benchmark to estimate the total number of people in attendance at the match.

Estimation Activity

For this activity you will need a picture with a group of objects / pictures arranged in an array. You could also have some other pictures that include pictures arranged more randomly, or that are different sizes. You could use a picture like the one below.

mental maths

  • Show the students the picture for about 30 seconds. Then ask them to estimate the number of lady bugs they saw.
  • This means students will need to estimate how many rows and columns of lady bugs there are.
  • Ask your students how they worked out their estimates.
  • Make a list of the different methods students used.

You could then use this technique to estimate other items such as:

  • Estimate the number of floor tiles in the room.
  • Estimate the number of bricks used on one side of a building.
  • Estimate the number of jelly beans in a guess the number of lollies competition.

Estimation Game

This is a game for 2 players. Players will need a calculator, 2 x 10 sided dice and a copy of a playing board, which includes numbers to suit the level of your students. An example is provided below.mental maths

  • The first player rolls the dice and must estimate the sum of the two numbers in the matching boxes. For example if the numbers on the dice were: 6 and 4, then the player estimates the sum of 228 + 574.
  • That player then selects the range that the estimate falls in.
  • The other player uses the calculator to work out the exact answer. If this answer falls within the range selected then the first player scores a point.
  • Play continues with players swapping turns.
  • The first player to get 5 points is the winner.
  • Remember the player that is estimating needs to do so mentally, so no paper and pencil to work out the estimates.

I hope you’ve enjoyed the mental maths strategies. Next up I’ll be sharing a heap of ideas for teaching about shape.

Click here to find more fun math games and activities

Graphic Credits: Graphics From the Pond

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