![]() Have a calculator handy if they need one to check your predicted answer. Practice this trick privately first, until you are confident you can do all the necessary calculations mentally, without errors. Here, we have 2781 + 20000 - 2, which is easy to do in your head. Therefore, the final answer will be two less than the first number, plus 20000. Since 9999 is 10000-1, no matter what the child writes, the sum will be (first number) + 20000 - 2. In this way, you make sure that whatever the child writes, his (or her) number plus yours makes 9999. Or, if the child wrote down 9393, you would write down 0606, since 9-9=0 and 9-3=6. ![]() To do so, subtract each digit of the child's number from 9. Then, whenever the child writes a number, you need to work out what number you will write. So with a two in front, your prediction becomes: In this case, that gives 2781 - 2 = 2779. To get your prediction, subtract two from from the child's number, and put a two in front. Then, it's your turn to predict the answer. Ask the child to write down a four-digit number. Even more importantly, I hope that they'll learn what I did about the hidden secrets of arithmetic when you show them how it works.įirst, explain the trick - that you will predict the outcome of an arithmetic sum. Hopefully they'll be as impressed as I was when they see it done. In the next few paragraphs, I'll explain how it works, so you can show the fifth-graders in your lives the same trick. But sure enough, his predicted answer was correct! How did he do it? My uncle wasn't a genius mathematician, yet his claim of 'magic' didn't sound convincing to me! How did this mathematical magic work? Now checking such a sum is not an easy thing for a fourth-grader! A calculator would have helped. ![]() He smiled, and again with no hesitation, wrote the final number in the sum. He took the pen, and without hesitation, he filled in the next number. Next, he explained there were still four more four-digit numbers to write in the sum, and we would take turns writing them, and I would start. How on earth could he predict it? I wondered. Then, he predicted the final result of the sum, and wrote it down. Here's how it worked.įirst, he asked me to write down a four-digit number, like so. Now, I know it wasn't magic at all, but by the end of the trick, it certainly seemed magical. He explained that by magic he could predict in advance what the result of an addition sum would be. I was visiting my grandparents, when my uncle got out a pen and paper, saying he had a math trick to show me. I must have been in about fourth or fifth grade.
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