If you want to impress your friends by reading their mind in advance, I bet that you want to learn this trick. This allows you to predict the sum in advance of the 5 numbers that you and your friend will write on a piece of paper. Note that the time your friend wrote the first number, you will already know the sum.
Below are the steps of the sum prediction math trick.
Ask your friend to write a 3-digit number. For example, he wrote, 428.
During this step, even if you haven’t written the additional four numbers yet, you will already know the answer. The answer is 2426.
How to get 2426? Subtract 2 from the first 428 (becomes 426) and then place 2 as the first digit. Note that the first of the sum or total will always be 2!
Ask him again to write another 3-digit number below what he had written. Tell him to align the digits. For example, he wrote 135.
Write your 3-digit number such that the sum of the number in Step 2 and your number is 999. That means that you write the your number such that each digit add up to 9 with the number in Step 2. For example, 2 pairs with 7, 3 pairs with 6, and 5 pairs with 4.
So, the number that you will write is 764.
Ask your friend again to write another 3-digit below the three numbers above. For example, he wrote 407.
Again, write your number such that the one in Step 4 and your number add up to 999.
Now, impress your friend by adding all the numbers. The sum is 2426, the number you predicted in Step 1!
Amazing isn’t it?
The sum prediction math trick works for larger numbers. Just be sure that all the numbers have the same number of digits.
Try doing this trick in 4-digit numbers, 5-digit numbers, or more.… You can also do this using 2-digit numbers.