L5 Solve Addition and Subtraction Missing Number Problems

Description

This Year 3 maths lesson on missing number problems and inverse operations helps pupils develop confidence in solving addition and subtraction equations with unknown values. By combining visual models, mental maths strategies and reasoning tasks, children learn how to use the inverse relationship between addition and subtraction to find missing numbers and check their answers.

The lesson begins with a starter activity revisiting previous Year 3 learning on addition, subtraction, place value and fractions. Pupils recall how inverse operations can be used to solve missing number problems and review examples from a previous lesson. Together, the class discusses how the order of numbers and the operation change when using the inverse, and considers whether using the inverse is always the most helpful strategy.

During the main teaching input, pupils explore a clear step-by-step approach to solving missing number problems. The teacher models how to:

• Verbalise the problem to understand what is happening mathematically

• Represent the numbers using a part–whole model to visualise the relationship between the values

• Use the inverse calculation to determine the missing number

Pupils are also reminded of previously learned mental maths strategies that can simplify calculations, such as adjusting numbers to make them easier to work with. For example, solving 782 − 352 by subtracting 350 first before adjusting the remaining amount.

Children then practise solving several missing number calculations on whiteboards, using both part–whole models and inverse operations to support their reasoning. The lesson also includes a word problem, where pupils must identify the relevant information before deciding which calculation is required.

In the independent activity, pupils take part in a fun and engaging missing number hunt around the classroom. Laminated problem cards are placed around the room and children record each problem in their books. For every calculation, pupils are expected to:

• Write the original calculation

• Show the inverse calculation used to solve it

• Include a visual representation, such as a part–whole model

• Calculate the correct answer

Teachers can choose between two versions of the activity: one without visible answers for assessment purposes, or one where answers are hidden under sticky notes so pupils can self-check their work.

The plenary focuses on identifying and correcting mistakes. Pupils analyse a missing number problem solved by Esin and identify where the error occurred. They explore two different strategies for checking the answer: using the inverse subtraction calculation or testing the value by completing the original addition calculation. This encourages pupils to compare methods and consider which approach is most efficient.

Throughout the lesson, carefully chosen questions encourage pupils to think deeply about inverse relationships, reasoning strategies and efficient calculation methods. Children are also encouraged to explain their thinking to a partner, helping to strengthen their mathematical communication skills.

This resource is ideal for Year 3 maths lessons on missing number problems, inverse operations, and reasoning in addition and subtraction, supporting pupils in developing flexible problem-solving skills and a deeper understanding of number relationships.