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SOURCE: https://www.easycalculation.com/math-facts/magic-number-3.html
Here is an interesting trick that lies on the power of number Three. Follow the steps below to learn the simple trick.
Let your friend to think of a number.
For example, assume number 6
Step 1: Ask your friend to add two with the number.
6 + 2 = 8
Step 2: Let him/her to multiply the resultant value with five.
8 x 5 = 40
Step 3: Tell him/her to add three with the result.
40 + 3 = 43
Step 4: Make her to multiply the resultant value with two and add it with four.
43 x 2 = 86 + 4 = 90
Step 5: Let him/her to divide the value with ten.
90 / 10 = 9
Step 6: Now, ask your friend to reveal the resultant number.
You can tell the number thought by your friend just by subtracting three from the resultant value,
9 – 3 = 6
See Excel file to make tests.