Truncating

When you begin estimating calculations, think of your mind as a Mighty Number Transformation Machine or MNTM for short. When you estimate, it can input any number, transform it, and output another number.

How does your mind do this? There are a few different techniques it can use. Today we will focus on the first way which is to shorten numbers to make them easier to work with. In math this is called truncating.

For example, when truncating the number 515 we remember how many groups of 100s there are. We truncate 515 to five.

Dogs like to think of truncating as biting off some digits. The idea behind biting off some digits is to get numbers with fewer digits that are easier to add, subtract, multiply, and divide. Of course even dogs, when they bite the number 45 and leave only a 4, have to remember that the 4 means 4 groups of 10.

So if you were trying to estimate what 432 + 812 = and wanted to use truncating, how would you do it?

You'd say 4 hundred + 8 hundred = 12 hundred = 1,200.

Truncating is a very fast way to estimate.

Comparing

Comparing is the heart and soul of estimating. In fact, when you estimate you are up to your ears in comparing.

To estimate measurements, you compare length, weight, volume, time, temperature and amounts. To estimate calculations you also compare. Luckily, you are an expert in comparing, whether you realize it or not. You know when your sister's slice of cake is bigger than yours, you know if your friend got more Halloween candy, you even know who has more space in the backseat.

Now you need to apply your expert comparing skills to estimating. It's all about comparing what you don't know to what you do.

For example, you don't know how tall the man on stilts is, but you do know how tall your dad is. You don't know how many hotdogs you can eat today, but you do know how many hotdogs you ate yesterday. You don't know what 24 x 4 equals, but you do know that 25 x 4 = 100 (because you know that four quarters make a dollar). You don't know how many gumballs are in the jar, but you can count how many are in a small section of the jar.

The key words for comparing are greater than, less than, or equal to.

The height of the man on stilts is greater than (>) the height of your dad. Your hunger yesterday is equal to (=) your hunger today. Lastly, 24 x 4 is less than (<) 25 x 4.