May 302013

10 Interesting Tricks in Mathematics

Mathematics is the figment of many people’s worst nightmares. But some people may really enjoy doing math and solving tricky questions. Regardless of the perception, mathematics is one of the most important subjects of study and yet, most of us tend to be really bad at it. The first thing that we forget about math is that it is simple if we practice it a few times. Who doesn’t like to have quick answers and solve great problems? The answer is: everyone. So, with that in mind here are the top 10 math tricks that will help you impress the other person.

1. 5 digit number trick:

Think of any number with 5 places or 5 digits. Multiply the number with 11 and then multiply the product of the number with 9091, the number that you will get as a result is the repetition of the 5 digit number. For example 12365 is our number, 12365*11=136015, 136015*9091=1236512365. This is a simple yet one of the most engaging math tricks if you are trying to show someone the magic of numbers.

2. Division by 5:

Division by five is also very simple, even if it is a larger number. Simply multiply the number by 2 and move the decimal point to one digit to its left. Take that number and multiply it by 2, for example 145 is our number then 145*2=290. Now move the decimal one digit to the left. The answer is 29. This comes in very handy when you have to do some fast calculations.

3. Multiplication by 5:

Multiplying by 5 with small numbers is easy and most people remember it. When it comes to larger numbers, people often get confused and make mistakes. Here is a quick way to multiply numbers by 5. Divide the number by 2, if the remainder is zero then add a zero to the end of the dividend, if the remainder is one then ignore the remainder and add 5 to the dividend. For example, 2345 is our number. 2345/2=1172 with one as remainder, ignore the one and add 5 to the dividend, 11725 is your answer

4. Multiply by 7, 11 and 13:

Think of any 3 digit number. Multiply the number by 7, the result by 11 and then the result by 13. You will get the product as a repetition of the same 3 digit number. For example, 121 is our number. 121*7=847, now multiply the product by 11, 847*11=9317. Multiply this product with 13, 9317*13=121121. The answer is a repetition of the digits of our original number.

5. Calculating percentages:

Calculating percentages is really simple; just remember that “per cent” is like saying parts of a hundred. For example 9%100 is 9. Now let us use this concept to find a percentage. Say, 15% of 70. We know that 15% of 100=15 and also 15% of 10=1.5. We also know that 15% of 50=7.5 as it is half of a hundred. We can write 15% of 70 as 15%of 50+15% of10+15%of10 which equals to 7.5+1.5+1.5=10.5

6. The same 3 digit number:

This is a simple trick. Think of any 3 digit number which has the same digits, for example 777. Add up the digits of the number in the face values, 7+7+7=21. Divide the 3 digit number with the sum of the digits in the number, i.e. 777/21, the answer is always 37.

7. Multiplying numbers by 9,99,999:

Multiplying any number by 9 is the same as multiplying a number to (10-1). Let’s see how this works. Take any number, say 56. Now, 56*99 is the same as 56(100-1), now open up the brackets, (56*100)-(56*1), this is the same as, 5600-56=5544. You can multiply any number with 9 or 99 or 999 or even 9999 using this method.

8. Any number:

Take any number and subtract 1 from the number. Multiply the result with 3 and then add 12 to the result after multiplication. Divide the answer by 3 and add 5 to the dividend. Now, subtract the number that you originally thought of from the answer. The answer will always be 8. For example, our number is 11. Subtract one, 11-1=10. Multiply by 3, 10*3=30. Add 12, 30+12=42. Divide by 3, 42/3=14. Add 5, 14+5=19. Subtract 11, 19-11=8.

9. Any number below 10:

Take any number below 10. Double the number and add six to the result. Halve the answer i.e. divide it by two. Subtract your original number from the dividend and the answer is always 3. For example, 6 is our number, 6*2=12, 12+6=18. 18/2=9. 9-6=3. The answer is the same for any number below 10 and the answer is always 3.

10. Multiply a two digit number by 11:

Take any two digit number, for example 27. Add the two digits of the number together; in this case the sum is 9. Place the sum of the two digits in the middle of the digits, and that is your answer. In case the sum comes up to more than 10, then add the digits in the ten’s place to the first digit and insert the second number in the middle. For example the sum of the two digits in 77 is 14. Add 1 to the first digit, i.e. 7+1=8, then insert the second number in between so that the answer is 847.

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