How to Multiply Challenging Decimals Easily

TL;DR

To multiply challenging decimals, first ignore the decimal points and multiply the whole numbers. Then, count the total number of decimal places from the original numbers and adjust the final product by placing the decimal point in the correct position, effectively dividing by the appropriate power of 10.

Transcript

Let's multiply 1.21, or 1 and 21 hundredths, times 43 thousandths, or 0.043. And I encourage you to pause this video and try it on your own. So let's just think about a very similar problem but one where essentially we don't write the decimals. Let's just think about multiplying 121 times 43, which we know how to do. So let's just think about this ... Read More

Key Insights

• ✖️ When multiplying decimals, simplify the problem by removing the decimals and performing regular multiplication.
• 🥇 To determine the number of decimal places in the final answer, count the number of decimal places in the original problem.
• ✊ Adjust the final answer by dividing by the appropriate power of 10, based on the number of decimal places.
• 👈 Multiplying by 100 is equivalent to moving the decimal point two places to the right, while multiplying by 0.01 is equivalent to moving the decimal point two places to the left.
• ✊ Division is used to adjust the final answer because multiplying and dividing by the same power of 10 cancels each other out.
• 🥇 The number of decimal places in the product should match the total number of decimal places in the original problem.
• ✖️ Understanding the relationship between decimals and whole numbers simplifies the process of multiplying decimals.

Questions & Answers

Q: How can we simplify the process of multiplying decimals?

To simplify multiplying decimals, you can temporarily remove the decimals, perform the multiplication as if the numbers were whole, and then adjust the final answer according to the number of decimal places.

Q: What do you need to do if you want to multiply a decimal by 100?

If you want to multiply a decimal by 100, you would move the decimal point two places to the right. This is because multiplying by 100 is equivalent to multiplying by 10 and then multiplying by 10 again.

Q: How do you multiply a decimal by 0.01?

Multiplying a decimal by 0.01 is the same as dividing the decimal by 100. You would move the decimal point two places to the left to get the correct product.

Q: Why do we use division to adjust the final answer?

When we initially ignored the decimals and performed regular multiplication, we essentially multiplied by a certain power of 10. To get back the correct product with decimals, we need to divide by the same power of 10. This is why we use division to adjust the final answer.

Summary & Key Takeaways

• The video demonstrates how to multiply decimals by first simplifying the problem by removing the decimals and performing regular multiplication.

• By understanding the relationship between decimals and whole numbers, you can easily multiply decimals by adjusting the decimal places.

• Dividing the final answer by the appropriate power of 10 allows you to go from a product without decimals to the desired product with decimals.