Max Maths, Year 5, Try it, Multiplying by 19 or 21 mentally

The 'Max Maths' Year 5 resource provides a mental arithmetic exercise focused on multiplying numbers by 19 or 21. The 'Let's Try It' section encourages students to perform mental calculations without the need for pen and paper. For instance, when multiplying 19 by 14, students are prompted to think of 20 times 14 first and then subtract 14 to get the answer. This technique leverages their familiarity with multiplying by 20—a simpler task—before adjusting the result to account for the actual multiplier of 19. Similarly, for multiplying 13 by 19, students would multiply 13 by 20 and then subtract 13 to find the correct product.

The exercise continues with multiplying 16 by 21, where students could first multiply 16 by 20 and then add 16 to get the final result. When multiplying 21 by 17, a similar strategy is applied: multiply 17 by 20 and add 17. The 'Let's Practise' section of the activity challenges students further by asking them to multiply other numbers by 19 or 21, this time showing their working out. This provides an opportunity for students to apply the mental strategies they've learned and demonstrate their understanding. To continue practicing, students are directed to workbook pages 75 to 76, where they can find additional exercises to reinforce their skills in mental multiplication.