Missing side worksheet
Six figures per sheet. The perimeter is given, one side is marked with a question mark, and the child works out how long that side is. Three levels, from taking the marked sides away to shapes that need two steps. Free, no account, no ads.
How to work it out
Two sides are marked. Take them away from the perimeter. New version prints a fresh set of six at the same level.
About these figures
The perimeter is given and one side is marked with a question mark. Each figure is drawn to match its own numbers, and lengths are in units rather than inches or centimetres, so the sheet prints correctly at any size and on any printer.
Find the missing side
Use the perimeter and the marked sides to work out the side marked with a question mark. Lengths are in units.
- Perimeter = 28 units? =units
- Perimeter = 28 units? =units
- Perimeter = 27 units? =units
- Perimeter = 18 units? =units
- Perimeter = 27 units? =units
- Perimeter = 26 units? =units
How it works
Perimeter is the distance all the way around a shape, so the sides always add up to it. That means the same fact can be read backwards: if you know the total and all but one of the sides, the one you are missing is whatever is left over. On the first level the child takes the marked sides away from the perimeter, and what remains is the answer.
Shapes where nothing is marked
On the equal sides level no side carries a number at all. Every side of a square is the same length, and so is every side of the triangles on that sheet, so the child shares the perimeter out between them. Noticing that the sides match is the whole job, which is why the numbers are left off on purpose.
Working towards an unknown
A question mark standing for a number the child has to find is the first step towards the letters used in algebra later on. Nothing here is written as an equation and no letters appear. The child works with a shape and a total, which keeps the reasoning about something they can see while the habit of solving for an unknown gets built.
Lengths are in units, not inches
Every length is given in plain units rather than inches or centimetres. That keeps the sheet honest: a printer set to fit-to-page shrinks the picture, and a sheet claiming real inches would then be wrong. Each figure is still drawn to match its own numbers.
Where it fits
This comes after a child can already add the sides up. If that is the step to practise first, try find the perimeter, which uses the same shapes the other way round. Naming shapes and counting their sides comes earlier still, on sides and corners.