Math tricks for fast calculation

TL;DR

Learn quick mental math techniques for multiplying numbers by 5, 25, and 125.

Transcript

good day welcome to the techmath channel what we're going to be having a look at in this video is a really fast instant method pretty much of multiplying by some pretty common numbers the numbers we're going to be having a look at is when you're multiplying a number by five or if you're multiplying by a number by 25 or even a number by 125 and how ... Read More

Key Insights

• 🐎 Mental math techniques can greatly speed up the process of multiplying numbers by 5, 25, and 125.
• #️⃣ Multiplying a number by 5 involves halving the number and adding a zero.
• #️⃣ Multiplying a number by 25 involves dividing the number by 4 and adding two zeros.
• #️⃣ Multiplying a number by 125 involves dividing the number by 8 and adding three zeros.
• 🧑‍🏭 Understanding the relationship between these numbers (5, 25, 125) and their factors (2, 4, 8) can help simplify the mental math process.
• 🗂️ For numbers that don't divide evenly, finding the closest number below that does divide evenly and adding the remaining amount can be used.
• 🐎 These mental math techniques can be used frequently and help speed up calculations in various situations.

Questions & Answers

Q: How do you multiply a number by 5 using mental math?

To multiply a number by 5, simply halve the number and add a zero to the end. For example, 46 * 5 would be calculated as (46 / 2) * 10 = 230.

Q: What is the technique for multiplying a number by 25 mentally?

To multiply a number by 25, divide the number by 4 and add two zeros to the end. For example, 36 * 25 would be calculated as (36 / 4) * 100 = 900.

Q: Can you explain how to multiply a number by 125 using mental math?

To multiply a number by 125, divide the number by 8 and add three zeros to the end. For example, 72 * 125 would be calculated as (72 / 8) * 1000 = 9000.

Q: What if the number doesn't divide evenly in the mental math technique?

If the number doesn't divide evenly, you find the closest number below it that does divide evenly and add the remaining amount. For example, for 27 * 5, calculate (26 / 2) * 10 + 5 = 135.

Summary & Key Takeaways

• This video teaches how to multiply numbers by 5, 25, and 125 using quick mental math techniques.

• To multiply a number by 5, halve the number, then add a zero to the end.

• To multiply a number by 25, divide the number by 4, then add two zeros to the end.

• To multiply a number by 125, divide the number by 8, then add three zeros to the end.