"' Why is it good to be able to calculate using mental math? (3)"

blog : 21-Jan-2022

Let's compare mental math with column method.

For example, when calculating 87+156, you can think of it in the following way

Write the 7 and 6 in the first place together and add them to get 13, then write the 1 in the top left hand corner. Then add 8, 5 and 1 in the tenth place to get 14, and write the 1 in the top left corner. Finally, add 1 and 1 in the 100th place to get 2. This gives an answer of 243.

If you are doing it by mental math, you can look at the whole number, and immediately see 8 and 15, which add up to 80 and 150, so the answer is 230; then quickly add 7 and 6 together in your head to get 13; then add these two numbers together again in your head to get 243.

Alternatively, you can take 87 as 90-3 and add 90 to 156 to get 246, then subtract 3 to get 243.

In other words, whereas in column method, the answer is obtained by adding one digit three times and writing down the number of digit increases, in mental math, the answer is obtained by recognising the number system and devising a quicker and better method.

Although mental math is more difficult, it is easier to start when the mind is flexible and then, once you are able to do it, we suggest to learn column method, which is a skill that can be used in any situation.