How often do you search for a calculator on your phone when you need to add or multiply numbers? In our era of digital technology, we have simply forgotten how to count quickly and immediately panic when we need to calculate something without a calculator.
In reality, mathematics is not such a scary subject. Like any science, it has its interesting secrets and tricks. Perhaps some of these mental calculation methods you learned back in school, or maybe, by reading them, you’ll teach your child mathematical tricks. AdmiGram.com will reveal to you the simplest secrets of mathematics, knowing which you will easily and quickly calculate in your mind.
How to calculate quickly or secrets of mathematics
Fast squaring
© Nathana Rebouças / Unsplash
This technique will help you quickly square a two-digit number ending in 5. Multiply the first digit by itself +1, and add 25 at the end. That’s it!
- 25^2 = (2 x 3) + 25 = 625
- 625
Calculating tips
If you need to leave a 15% tip, there is a simple way to do it. Calculate 10% (divide the number by 10), then add the resulting number to its half, and you get the answer:
- 15% of 25 = (10% of 25) + ((10% of 25) / 2)
- 2.50 + 1.25 = 3.75
Complex multiplication
If you need to multiply large numbers, and one of them is even, you can try regrouping them to get the answer:
- 32 x 125 is the same as:
- 16 x 250 is the same as:
- 8 x 500 is the same as:
- 4 x 1,000 = 4,000
Multiplication by 11
© Chris Liverani / Unsplash
We all know that when you multiply by 10, you add 0 to the number. But did you know there is a similarly simple way to multiply a two-digit number by 11? Here it is:
Take the original number and imagine the gap between the two digits (in this example, we use the number 52):
- 5_2
Now add the two numbers and write them in the middle:
- 5_(5+2)_2
Thus, your answer is 572.
If the sum of the numbers in parentheses is a two-digit number, just remember the second digit, and add the unit to the first number:
- 9_(9+9)_9
- (9+1)_8_9
- 10_8_9
1089 – This always works.
Systematized multiplication rules
- Multiplication by 5: Multiply by 10 and divide by 2.
- Multiplication by 6: Sometimes it’s easier to multiply by 3 and then by 2.
- Multiplication by 9: Multiply by 10 and subtract the original number.
- Multiplication by 12: Multiply by 10 and add the original number twice.
- Multiplication by 13: Multiply by 3 and add the original number ten times.
- Multiplication by 14: Multiply by 7, then by 2.
- Multiplication by 15: Multiply by 10 and add the original number five times, as in the previous example.
- Multiplication by 16: If you want, multiply by 2 four times. Or multiply by 8 and then by 2.
- Multiplication by 17: Multiply by 7 and add the original number ten times.
- Multiplication by 18: Multiply by 20 and subtract the original number twice.
- Multiplication by 19: Multiply by 20 and subtract the original number.
- Multiplication by 24: Multiply by 8 and then by 3.
- Multiplication by 27: Multiply by 30 and subtract the original number three times.
- Multiplication by 45: Multiply by 50 and subtract the original number five times.
- Multiplication by 90: Multiply by 9 and add a zero.
- Multiplication by 98: Multiply by 100 and subtract the original number twice.
- Multiplication by 99: Multiply by 100 and subtract the original number.
image on top: Jim Kelly / Flickr
