I have always had a fascination with numbers. I don’t know why, other than numbers make sense. History doesn’t always make sense; politics rarely make sense, but two plus two equals four, and that makes perfect sense to me. You just can’t argue with that!
Anyhow, my captivation with numbers has led me to learn three ways a person can add or subtract numbers quickly. These skills are valuable in many areas of our lives. They’re helpful in conducting business transactions, counting out change at a yard sale, and figuring out how much money you need when you take your three kids to the movies, just to name a few examples. Have you ever wondered if the mechanic added up your car repair bill right? How about the busy waitress that served your family dinner last night? Were you able to quickly tally up the bill to make sure you weren’t overcharged?
You can see how handy, as well as economical, being able to add and subtract whole numbers can benefit your life!
1. The Divide and Conquer Method
You’re probably familiar with the old-age military tactic known as, “Divide and Conquer.” It means that to beat your enemy, you need to divide them up into smaller groups and then clobber them. Smaller groups are easier to beat than a single large clump. When you use the same tactic with whole numbers, it works just as well!
The first method is for adding whole numbers in a record amount of time. Most numbers can be tallied up in your mind if you can visualize them. Let’s add 56 and 37 together without using a calculator. The process will be fast and easy once you get the hang of it.
We’ll need to divide, or separate, the mathematical numbers and then add the parts together to come up with a total sum. Separate 56 into 50 and 6 in your head. 37 also becomes 30 and 7. Now add the higher numbers – 50 and 30 together. 50 + 30 = 80. Add 6 to that, and then the 7, and you instantly have the sum figured out. 80 + 6 + 7 = 93.
2. Add ‘Em Up Method
The second method is a fun way to add a line of single-digit numbers in your head. Let’s use
3 + 7 + 6+ 4 + 5 + 5 + 2 + 8 + 1 + 9 as an example. Instead of looking at the whole numbers one at a time like we did when we used the first method, we’ll now switch gears into reverse. We will now clump the numbers into groups of ten and then add the groups together.
Looking at the example, 3 + 7 equals ten, as does the next four groups of single-digit numbers.
Therefore, 10 X 5 = 50. If the line of numbers you’re adding up has whole numbers that exceed 10, then you just need to add in the remainders.
3. Take It Away Method
Subtracting whole numbers in your head is a little harder than adding them together. But, never fear! You can still do this method with a little bit of practice. It takes much less time to subtract even the largest mathematical numbers in your mind as opposed to: first, locating a pencil and a paper; second, writing down the numbers; subtracting the numbers one by one and until you finally arrive at an answer!
To use this method, just think of a cashier counting out change to a customer. Simply add instead of taking away from. Let’s subtract 367 from 1,000. You can do this quickly by adding on numbers too 367 until you reach the 1,000. 367 + 3 = 370 + 30 = 400 + 600 = 1,000. Therefore, 1,000 minus 367 equals 3 + 30 + 600 = 633. Neat, huh?