🧮 שלושה קסמי חשבון בראש

Mental math can actually be a lot of fun once you know a few clever shortcuts. Here are three tricks that will make your friends think you're secretly a calculator. Trick one: multiplying by 11. To multiply any two-digit number by 11, separate its two digits and place their sum in between. For example, 34 times 11: split it into 3 and 4, add them together to get 7, and slide that in the middle - giving you 374! If the sum is bigger than 9, like with 58 times 11, you carry a digit: 5 and 8 add up to 13, so you write down the 3 in the middle and add the extra 1 onto the 5, giving you 638. Trick two: quick percentage estimates. To roughly calculate 15% of a number, first find 10% (just move the decimal point one place to the left), then add half of that, which is 5%. For example, 15% of 80: 10% of 80 is 8, half of 8 is 4, and 8 plus 4 equals 12. That's exactly 15% of 80. Trick three: squaring numbers that end in 5. Take the digit (or digits) before the 5, multiply it by the next whole number up, and stick 25 onto the end. For example, 35 squared: take the 3, multiply it by 4 (the next number), which gives you 12, then add 25 at the end - giving you 1225. Sure enough, 35 times 35 really does equal 1225. With a little practice, all three tricks become automatic - and then you can genuinely impress everyone at your next birthday party.