Easy Mental Math
>> Sunday, January 23, 2011
The problem is quite simple: you have a bunch of items, most of which are priced below USD 100, and you want to know how much they're worth all-in-all. In short, you need to do some mental addition. Some people tend to shy away from this because they think is something that would require a Nobel laureate. However, that is absolutely not the case.Okay, let's start with simple addition of two-digit numbers. Any two-digit number comes in the form XY, where X is the first digit and Y is the second. Now, suppose we have two 2-digit numbers that we need to add: XY and ST. Sounds tricky? Here's a concrete example.
Download Exam Drill of Mathematics for Senior High School
Let's Get it On!
If a big bag of peanuts costs USD 27 and a pound of high-quality lettuce costs USD 16, then let's try to get the total amount.
Here's a quick rundown of what you would do.
1: Problem: 27 + 16
2: Split: (20 + 6) + (10 + 6)
3: Rearrange: (20 + 10) + (7 + 6)
4: Add: (30) + 13
If you would have to work on multiple numbers, the process is the same - except that you can choose to add the first two items first, and add the third item to the sum of the first two. Here's a quick example.
Not Just Two Pieces?
Suppose we also threw in a bottle of mayonnaise worth USD 12 to the bag of peanuts and the lettuce.
We first add the peanuts and lettuce, which gets us USD 43. 1: Problem: 43 + 12
2: Split: (40 + 3) + (10 + 2)
3: Rearrange: (40 + 10) + (3 + 2)
4: Add: (50) + 5
Note that the decimal places (that is, the "cents" part of the price tag) was not included in this calculation. If we included it then it would be too complicated. However, what you can do to compensate for the inaccuracy is to round the price up to the nearest whole number. For example, if the price of mayonnaise is USD 12.55, then round it up to USD 13.
As you add more and more stuff into your shopping cart, just do the same process over and over. You'll be surprised that after a little bit of practice (which takes less than 20 minutes), you'll feel like you're just one exam short of being a rocket scientist!
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