Easy Mental Math: Unleash The Little Einstein While Grocery Shopping! 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. The trick to this is to add X and S, and then Y and T, and combine the result.

Sounds tricky? Not actually. Here’s a concrete example.

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)

5: Add again: 43. That is, the total amount is USD 43.

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. Hence, we are left with the relatively simple problem of adding 43 and 12.

1: Problem: 43 + 12

2: Split: (40 + 3) + (10 + 2)

3: Rearrange: (40 + 10) + (3 + 2)