Mental Math Tricks: Multiply Numbers in Your Head

Ever find yourself in a situation where you need to quickly multiply numbers, but a calculator isn’t handy? Or maybe you just want to impress your friends with your mental math skills? This blog post will teach you a fun and easy trick to multiply certain pairs of numbers in your head. It’s a great way to boost your mental agility and have some fun with math!

The Trick: Multiplying Numbers Close to 100

This trick focuses on multiplying numbers that are close to 100. Let’s break it down step by step:

1. Find the Difference: Determine how far each number is from 100. For example, if you’re multiplying 98 by 96, 98 is 2 away from 100, and 96 is 4 away from 100.
2. Add the Differences: Add the differences you found in step 1. In our example, 2 + 4 = 6.
3. Subtract from 100: Subtract the sum from step 2 from 100. So, 100 – 6 = 94.
4. Multiply the Differences: Multiply the differences from step 1. In our example, 2 x 4 = 8.
5. Combine the Results: Combine the result from step 3 with the result from step 4. This gives you the final answer: 9408.

Let’s Try Another Example:

Let’s say you want to multiply 103 by 97.

1. Difference: 103 is 3 away from 100, and 97 is 3 away from 100.
2. Add Differences: 3 + 3 = 6.
3. Subtract from 100: 100 – 6 = 94.
4. Multiply Differences: 3 x 3 = 9.
5. Combine: 9409 is the answer.

Why Does This Work?

This trick works because it cleverly breaks down the multiplication into smaller, easier steps. Let’s look at why it works using algebra:

(100 – a) * (100 – b) = 10000 – 100a – 100b + ab

Notice that the first three terms are similar to the steps we followed in the trick. The last term, ‘ab’, is the multiplication of the differences, which we add at the end.

Practice Makes Perfect!

The more you practice this mental math trick, the faster and more confident you’ll become. Try it out with different numbers near 100. Challenge yourself and your friends! You’ll be surprised at how quickly you can master this handy trick.