Multiplying by multiples of 10 | Multiplication and division | Arithmetic | Khan Academy

TL;DR

Learn two simple techniques to multiply numbers efficiently.

Transcript

Let's see if we can figure out 3 times 60. Well, there's a couple of ways you could think about it. You could literally view this as 60 three times. So you could view this as 60 plus 60 plus 60. And you might be able to compute this in your head. 60 plus 60 is 120, plus another 60 is 180. And you'd be done. But another way to think about this is th... Read More

Key Insights

• #️⃣ Multiplying numbers can be approached using strategies like repeated addition or breaking down numbers into smaller factors.
• ✖️ Recognizing patterns and relationships between numbers can simplify multiplication.
• ✖️ The order of multiplication does not affect the result when multiplying three numbers.
• 🍳 Breaking down numbers into their components helps in performing mental calculations.

Questions & Answers

Q: How can 3 times 60 be computed mentally?

One way is to add 60 to itself three times, resulting in 180. Another approach is to break down 60 into smaller components (6 times 10) and multiply accordingly: 3 times 6 equals 18, and multiplying that by 10 gives 180.

Q: What is an efficient method for multiplying 50 by 7?

Recognizing that 50 is equal to 10 times 5, we can multiply 5 by 7, which equals 35. Then, adding a zero at the end gives the answer 350.

Q: Why is the order of multiplication irrelevant when multiplying three numbers?

The order of multiplication does not matter because multiplying three numbers is associative. In the example, we can multiply 3 by 6 first and then multiply that result by 10, or vice versa, to calculate 3 times 60.

Q: How can breaking down a number simplify multiplication?

Breaking down a number into smaller components allows for easier multiplication. In the example, 50 is decomposed into 10 times 5, making it simpler to multiply 5 by 7 and then multiply by 10 to find the product.

Summary & Key Takeaways

• The video demonstrates two methods for multiplying numbers: adding a number to itself multiple times and breaking down a number into smaller components.

• Method 1: Multiplying 3 by 60 can be done by adding 60 three times, resulting in 180.

• Method 2: Multiplying 50 by 7 can be simplified by recognizing that 50 is equal to 10 times 5. Multiplying 5 by 7 gives 35, and adding a zero at the end produces the answer 350.