Magic Addition Trick: Predicting Sum of a series of 5-digit numbers

Ask someone to write a number, say a 5-digit number. (Can be a 2-digit.....3-digit.....4-digit....etc...…).

Suppose the number written is 78513.

Now, tell the person that you are each going to write down 2 more 5 digit numbers and add them, but before you do, you are going to write down the answer on a piece of paper and keep it folded.
You obtain the answer by subtracting 2 from the above number and placing a 2 before the first digit
- thus 78513 become 278511 for the answer.

Now ask the person to write two more 5-digits number down, either at once or in succession with you. Either way, he must go before you.

Suppose he writes 27569.

So you now have...

Now you write a five-digit number below it in such a way that each digit is 9 minus digit above. You now have...


Then if he adds 45732, you add below it 54267. Note that you decided the number by subtracting each of his digits from 9.

Predicting-sum-of-a-series-of-5-digit-numbersThus, you now have.....

Now, ask him to add all the number and he gets 278511.

Show him the number which you had written as the answer to this addition earlier in the folded paper and … you're a hero!

Another example:

Suppose the number written is 746. You write 2744 on a piece of paper for the answer and fold it up.

Original number             746
Their first number          325
Your first number           674 (999-325)
Their second number      841
Your second number       158 (999-841)
Total is                        2744

They unfold the paper and you're a hero!

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Mental Math for Faster Calculation

Mental Math for Faster Calculation
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