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SOURCE: https://www.easycalculation.com/math-facts/finding-out-the-missing-digits.html
Here is an interesting trick to find the missing number. Follow the steps below to learn this simple trick.
Step 1: Let your friend to write down 4 to 5 digit numbers.
For example, 39861
Step 2: Ask your friend to sum up the digits.
3 + 9 + 8 + 6 + 1 = 27
Step 3: Now ask him/her to subtract the step 2 result from the main value
39861 – 27 = 39834
Step 4: Ask you friend to leave one digit and say all other digit from the result.
Let us keep that he left 8 and says the remaining number 3 9 x 3 4 to you.
Step 5: You can find the left out digit with the simple trick
Just add up all the digits given by your friend
3 + 9 + 3 + 4 = 19 = 1 + 9 = 10 = 1+0 = 1
Now subtract from 9, the result is 9-1 = 8
Note: How it works. Any number subtracted from the sum of its digits will be a multiple of Nine. That’s the magic of number nine.
