Often children are asked in tests to solve problems where numbers are missing e.g. ? + 234 = 782, 7 x ? = 371 etc. It is therefore important that they remember the following rules which will enable them to solve this type of question.

1. Where the missing number is at the start of a calculation. Here in order to solve this type of problem you start with the answer and perform the opposite operation to it to find the missing number.

e.g. ? + 78 = 235 To solve it start with the answer 235 and do the opposite of adding 78, which is subtracting 78. The missing number is therefore 235 - 78 = 157, so 157 + 78 = 235.

? x 9 = 477 To solve take the answer 477 and do the opposite of multiplying by 9, which is dividing by 9. 477 divided by 9 is 53, so 53 x 9 = 477

2. Where the missing number is in the middle of an add or subtract sum. Here in order to solve the problem you need to find the difference between the 2 numbers given i.e. subtract the smaller number from the larger one.

e.g. 234 + ? = 578 To solve do 578 - 234 which is 344, so 234 + 344 = 578

793 - ? = 562 To solve do 793 - 562 which is 231, so 793 - 231 = 562

3. Where the missing number is in the middle of a multiply or divide calculation. To solve this type of problem you need to divide the larger number given by the smaller one.

e.g. 513 divided by ? = 9 to solve do 513 divided by 9 which is 57, so 513 divided by 57 = 9

7 x ? = 476 to solve do 476 divided by 7 which is 68, so 7 x 68 = 476.

In order to practice using these rules I have a worksheet which may be downloaded below. If further questions are required for consolidation then just make up you own questions in a similar way and get your child to show what working they have done to arrive at the answer.

Download Missing Number Problems

Great tip. Thanks for sharing the solution!

Posted by: GMAT Math | 07/29/2011 at 06:21 AM