Have you needed to add or subtract two numbers very quickly, and didn't have a calculator nearby, or felt too tired to compute the sum or difference in your head? There are many techniques that can be used that are especially helpful for those who need a helping hand!
Let's work a couple examples.
What is the sum of 121 + 98? There are a few people that can quickly compute this within a second or two. The easiest way to simplify this calculation is to add 2 to 98, which bumps it to 100. If we add 2 to the one number, we must subtract 2 from the other number, decreasing it from 121 to 119.
Now, what is the sum of 119 + 100? That's right! It is 219.
Here's another one to try. What is the sum of 77 + 36? You can increase 77 to 80 by adding 3, and also decrease 36 by 3, which is 33. The sum is 113.
We could have easily adjusted the 36 to 40 by adding 4, and decreasing 77 by 4 to 73. 40 + 73 = 113.
Many of us refrain from adding numbers in our head, because we don't have experience, or we prefer to write it on paper where we can see it, but also feel more confident that we won't make a mistake.
This is just one of many tips and shortcuts that I will share with you as you continue in your quest to love math!
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