Ask a friend to write any three digit number on a sheet of paper.
Ask him/her to multiply the number by 7, then by 11 and finally by 13. (You can give him/her a calculator)
You will still get the answer quicker than your friend.
Trick: Just write the three digit number twice to get the answer.
Example: Let 452 be the number chosen by your friend. 452 x 7 x 11 x 13 = 452452. That is the same as 452 written two times.
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