Cool Multiplication Trick Part 1

We have learned quite a number of multiplication tricks now and in this post, I am going to teach you another multiplication trick which you can use to calculate faster and share with your friends. This multiplication trick is quite similar to squaring a number ending in 5.

The conditions to perform this trick are

(a) the sum of the ones digit is 10.

(b) the other digits (tens, hundreds, and so on) are the same.

Example 1: 23 × 27

This example fits the two conditions above. For (a), 3 + 7 = 10. Then, for (b) the tens digits are the same.

The Math Trick

Step 1:  Add 1 to one of the tens digit, then multiply to the other tens digits.  Continue reading

Why the Addition of Dissimilar Fractions Trick Works

In the pervious post, we have learned a math trick on addition of two dissimilar fraction. This is done by “cross multiplying” the numerators and denominators of the fractions as shown below (read the previous post for more details). In this post, we discuss why this trick works.

Remember: It’s cool to know the math trick, but it’s even cooler, or should I say awesome, to know why the math trick works.

add fractions

Now, why does this trick works? Will it work every time?  Continue reading

How to Add Two Fractions Faster

Fractions whose denominators are the same are called similar fractions, otherwise they are called dissimilar fractions. The fractions 1/9 and 7/9 are similar fractions, while 3/4 and 2/3.

Adding similar fractions is easy. Just copy add the numerator and then copy the denominator. For example,

1/9 + 7/9 = 8/9.

Adding dissimilar fractions is a bit more complicated. You have to get the Least Common Multiple (LCM) of the denominators. For example, if we want to add 3/4 and 2/3, we get the LCM of 4 and 3 which is equal to 12. You then change the given to equivalent fractions. The addition becomes

9/12 + 8/12 = 17/12.

Shortcut: How to Add Two Fractions Faster

We can use a shortcut to add to two add fractions.  We will only discuss dissimilar fractions because similar fractions are too easy to add. Below are the steps for the shortcut 3/4 and 2/3 Continue reading

Mental Math: How to Subtract Numbers Faster

In the previous post, we have learned a faster way to add numbers near multiples of 10. In this post, we are going to learn to subtract numbers faster, but first let’s review some basic terms.

In the subtraction

8 – 6 = 2

8 is the minuend, 6 is the subtrahend and 2 is the difference.

In subtracting numbers, numbers may be added to the minuend and subtrahend in order to simplify calculations. The strategy is to change the subtrahend to multiples of ten, hundred, thousands, etc. Doing this will speed up calculation and with enough practice, may be done mentally. Here are some examples.

Example 1

1.) What is 55 – 18?

In this case, 18 is near 20, so we can add 2. If we add 2 to 20, we should also add 2 to 55. So, the expression becomes

(55 + 2) – (18 + 2).

Simplifying, we have 57 – 20 = 37. And really, 55 – 18 = 37.  Continue reading

Mental Math: Adding Numbers Near Multiples of 10

People who are very good at mental math calculations are not all gifted. Some of them just know simple strategies in order to calculate numbers easily and fast.

In this post, I am going to teach you a math trick on adding numbers that will simplify and speed up calculations. With enough practice, you can even use this strategy to perform mental calculations.

This strategy uses numbers that are near multiples of tens, hundreds, thousands, and so on. We can add a certain number to one addend and subtract that number to another addend in order to make one of the addends a multiple of 10. Sounds complicated? Not really.

Example 1:  49 + 36

This looks really hard to calculate mentally, but it’s easier than you think. First, we see that 49 is nearly 50. So, we can add 1 to 49.

This becomes 50 + ? Well, we add 1 to 49, so we have to subtract 1 from 36. So, 36 becomes 35. Therefore, the addition  Continue reading