Mental maths magic

Proficiency at mental maths is a rare skill. It seems most schools or colleges don’t teach us how to calculate quickly and easily in our heads. Having said that, I worked with a student last year who started every school maths lesson with a short mental maths test. Not surprisingly, this student was brilliant at calculating in his head, and thoroughly enjoyed doing it too.

Once you master mental maths, it becomes fun. Rapid mental maths calulating is a skill anyone can learn, but like all skills, it takes practice. It doesn’t happen without effort. And just like mastering any subject, it’s incremental improvements that really work. It’s the way our brains function. The fastest student can even beat calculators to the answer. Just imagine how good that would be in tests and exams.

Let’s look at a few simple techniques: 2 and 3-digit multiplication is easy to do, once you know how. Multiply 45 times 11. Add 4 to 5 and you get 9. Insert it between the 4 and 5, and you get 495. That’s the answer. Or multiply 76 times 11. 7 add 6 is 13. 7 plus 1 is 8. The 7 becomes an 8, and insert 3 between the 8 and the 6. The answer is 836. One more; 314 times 11 = 3, 3+1, 1+4, 4 = 3454 is the answer. We added the 1st and 2nd digits together, and the 2nd and 3rd digits.

We can do squares too. 35 squared is 35 times 35. So 3 times (3+1) is 12. 5 times 5 is 25. The answer is 1225. And 85 squared is 85 times 85. So 8 times (8+1) is 8 times 9, which is 72. 5 times 5 is 25. So the answer is 7225.

Addition can be simplified too. The key is to work from left to right instead of the way we’ve been taught, which is right to left. So you are dealing with the most significant digits first. Let’s try 2-digit addition. 47 + 32 is 47 +30 = 77. 77 + 2 is 79. Try adding 67 and 28. 67 + 20 = 87. 87 + 8 = 95 (7 + 8 = 12).

3-digit addition takes just a little longer. 538 + 327 is 538 + 300 = 838. 838 + 20 = 858. 858 + 7 = 865. You break it down. It get easier as you approach the answer, and there really isn’t much to remember in your head. Let’s try one more. 858 + 634. 858 + 600 = 1458. 1458 + 30 = 1488. 1488 + 4 = 1492.

If you want to learn some more, take a look at ‘think like a maths genius‘. It’s faster and seems like magic compared to the way most of us were taught at school.