Calculate the cross sum in elementary school
Calculating the cross sum in elementary school can be a bit of a challenge. With a child-friendly explanation and a few small examples, this is quickly passed.
Check sum in elementary school - definition and meaning
- The name already suggests what the checksum is: It is the sum of digits that are placed diagonally next to one another.
- In order to calculate a sum, the adjacent digits must be added together, i.e. calculated as a plus. The first calculation of this kind that every elementary school student learns is 1 + 1 = 2.
- The checksum whether in primary school or later, can be calculated just as easily as these addition problems. The checksum of 111 is therefore 1 + 1 + 1 = 3. Just like the number of 12, where 1 + 2 = 3 is calculated.
- In addition to the normal cross-sum, in which the digits of a number are added to a total, the single-digit cross-sum can also be requested. This is added until there is only one digit left. The cross-sum of 83, which is formed by 8 + 3 = 11, becomes the single-digit cross-sum 2 by adding the result further. The full calculation for this is 83 = 8 + 3 = 11 = 1 + 1 = 2.
- Being able to calculate the cross sum quickly and reliably from elementary school onwards helps when applying divisibility rules 3 and 9. Explain to your child that the checksum can simplify other calculations - this motivates them to study and practice.
Iterative checksum - explanation
When you hear the phrase "iterative checksum," the first thing you probably think ...
Explaining checksums in a child-friendly manner - instructions
- Start easily by introducing the checksums in the same way as you did additions. The cross sum of 11, so 1 + 1 = 2 is a good place to start.
- Use a pen and paper or small sweets that you add up.
- If the calculation of the checksum works quite well with tools and simple tasks, switch to longer rows of digits. Here, too, start again quite simply, for example with 1111 or 12345.
- If your child can easily solve the long tasks with aids, go to Mental arithmetic and incorporate tasks into everyday life.
- House numbers, license plates of cars, price labels, birthdays and much more offer numerous sequences of digits with which you can practice calculating the checksums. Make a game out of it, for example "Who can do the task faster?" and learning becomes fun.
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