# Make estimates of the results of simple calculations, without using a calculator

A classic mistake made by students is to think that when asked to estimate an answer if they work it out exactly they will get more marks. This can be further compounded by students becoming programmed to think that anything done in science (and particularly in physics) wit numbers needs an equation that they plug numbers into. By seeing these calculations and their answers as a process rather than necessarily meaning anything can lead to students making calculation mistakes they do not even notice. Example might include working out the thickness of a wire at 25000m or the speed of a car at 0.0025m/s.

In the revised national curriculum (2014) there are some specific statements that require students to be familiar with ‘common values’ for quantities such as the speed of sound or walking or cycling and so their ability to be able to make estimates and have reference points is important. In Biology it is likely that they will be able to make an estimate of the size of cells and in Chemistry the size of atoms and molecules.

Science is therefore an ideal opportunity to discuss with students the purpose of estimation in real life situations. Ensure pupils appreciate that in most cases the purpose of choosing approximate values is to produce a calculation that can be done mentally. Using estimation in the context of the Science classroom gives them the opportunity to discuss the 'sense' of their answers. If pupils struggle with the mental calculation then encourage them to round a bit more.

Give or ask for some examples of where an exact number is not needed or may be impossible to determine, for example the distance travelled between two towns. Discuss why a number rounded to the nearest 10, 100 or 1 000 is sometimes enough, for example the size of a crowd at a football match.

Solutions should make sense in terms of the context and cannot be more accurate than the input data. Units should be made clear.