Percentage Math Trick 3: Making Use of Fractions

In the previous two posts, we have learned two types of calculations about percentage: ignoring the percent sign and making use of 10%. In this post, we learn another math shortcut that is very useful in speed calculations about percentage.

One of the easiest ways to calculate for a percentage of a number is to convert percent into fractions. For example, 50% is equivalent to 1/2 so instead of multiplying the number by 0.5, you can just multiply by one half (or equivalently) divide by 2. Here are some examples.

Example 1

What is 50% of 284?  Continue reading

Percentage Math Tricks: Making Use of 10%

In the previous post, we have learned how to calculate the percentage of a number by ignoring the percent sign. We continue our discussion on the tricks in getting the percentage with a number by making use of 10%.

Calculating 10% of the number is one of the easiest calculations in percentage. To calculate 10% means to get 1/10 of that number. This can be done easily mentally: 10% of 200 is 20 and 10% of 85 is 8.5. As we can see, we just eliminate 0 in the ones place if the number ends with 0 or move the decimal point one digit to the left.  So how do we make use of 10% in making calculations?

Example 1: Multiplies of 10%

What is 20% o 750? Continue reading

Percentage Math Trick 1: Ignoring the Percent Sign

Discounts and interests are some of the practical application of percentage. We often see 15% discount in the things we buy in stores and we also hear interests of money on loans. But how can we calculate percentage easily? Here are some math tricks on calculating percentage.

Percentage Math Trick 1: Ignoring the Percent Sign

The first strategy is to ignore the percentage sign, multiply the two numbers. And then, after getting the product, divide it by 100. Dividing by 100 is so easy, just move the decimal point to digits to the left or if there are two zeroes or more on the right, just eliminate the two zeroes.

Example 1:

What is 20% of 300?  Continue reading

Mental Multiplication: 2 Digit Numbers by 1 Digit Numbers

Mental multiplication is hard, but there are strategies and tricks that you can use to do this.  In a previous post, we have learned an alternative way on how to multiply 2-digit number by 2-digit number faster, and in this post, I am going to share another way, on how to do mental multiplication of of 2-digit numbers by 1-digit numbers. In this strategy, we will split the numbers into tens and ones, multiply separately, then add the products. Let’s have our first example.

The Math Trick

Example 1: 25 × 7

In this example, we split 25 into tens and ones 20 and 5. Then, we multiply both of them by 7.

Step 1: 20 × 7 = 140

Step 2: 5 × 7 = 35

Adding both products, we have  Continue reading

How to Multiply by 9, 99, 999, 9999 Faster

Before I explain the previous post about multiplication, I would like to discuss first multiplication by 9, 99, 999, 9999 or any number whose digits are all 9. For example, how do we multiply 87 × 99? To multiply by numbers whose digits are all 9, we just add 1 to 9, 99, 999, 9999 and so on and then subtract the number that we are multiplying with it.

Example 1: 7 × 9

1. 7 × 9 = 7 × 10 – 7

= 70 – 7 = 63

The reason that we subtract 7 is that because 9 = 10 – 1 and that 7 × 9 = 7 (10 – 1) = 70 – 7 = 63.

Example 2: 4 × 99

4 × 99 = 4(100 – 1) = 400 – 4 = 396

Example 3: 18 × 999

18 × 999 = 18(1000 – 1) = 18000 – 18 = 17982  Continue reading