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News from Mathnasium of Pflugerville

5 Mental Math Tricks That Make Life Easier

Jul 24, 2017

Original Article:


Do you struggle to double recipes, split restaurant bills, calculate discounts, or prepare your taxes? Learn these tricks for addition, subtraction, multiplication, division, and percentages to make these and other everyday tasks much easier. Each can help you save time and gain confidence.

1. Addition

Useful for cooking, scheduling activities, and calculating your spending while shopping.

When adding a list of small numbers, forget working from left to right and instead look for pairs that add to 10. For example, here’s a task:


By locating pairs that equal 10 and then tacking on anything leftover, the problem becomes much more manageable. The string becomes:




2. Subtraction

Useful for making change, determining your credit balance, and more.

“Big-number” subtraction can be intimidating when looked at as a whole. It’s much easier to swallow when broken into more digestible chunks. Let’s say we need to calculate this:



Don’t give up just yet. One approach to solving this problem without borrowing numbers is to count up from the smaller number in the equation in steps until you reach the larger number. (It’s typically easiest if those steps reach numbers that end in zero.)

Then add each step together to get the answer. It looks like this:


3. Multiplication

Useful for party planning, preparing taxes, and calculating investments.

As with addition, multiplication becomes much more manageable when done in 10’s. Here’s what we mean:


To simplify, break up 73 into a multiple of 10 (70) plus 3, and think of the problem like this (allowed by the distributive property):


4. Division

Useful for splitting restaurant bills and figuring out the number of calories in a serving.

The goal in division is to whittle down the numbers as much as possible before completing the given problem. Why? Because it’s almost always easier to work with smaller numbers. Here’s an example:


Both numbers are even, so we can begin dividing them by 2 to get to the smallest possible version of the equation.


A similar rule also applies to odd numbers. They often can be whittled down by 3. For example, 105 ÷ 15 becomes (105 ÷ 3) ÷ (15 ÷ 3), or 35 ÷ 5 = 7

5. Percentages

Useful for tipping and calculating sale discounts.

Mentally calculating percentages comes into play most often when calculating tips, so we love the “10-percent hack” because it provides a great tipping baseline.

To calculate 10 percent, the decimal simply moves one place to the left. So let’s say a restaurant bill is $41.50.


So, about $4. You can then use that information to calculate your tip. If you want to leave a 20 percent tip, you simply need to double it, which is about $8. And if you want to leave a 15 percent tip, you just add half of the 10 percent to the original 10 percent, which comes to around $6.


To sum up (pun intended), we hope everyone finds use for these quick tips in their everyday lives and has a happy math-filled month!

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