Multiply by 10s
🧠 What is it and Why is it Useful?
Multiplying by 10s (like 10, 20, 30, etc.) is a super-fast way to count large numbers. It helps you solve problems quickly without counting one-by-one. You use it when counting groups of ten, like boxes of 10 crayons or bags of 20 marbles!
📝 How to Solve Problems: Step-by-Step
- Step 1: Look at the basic fact. Multiply the digits in the ones place first. (e.g., for 4 × 20, first do 4 × 2).
- Step 2: Count the zero. Look at your 10s number and count how many zeros it has.
- Step 3: Attach the zero. Take the answer from Step 1 and attach the zero from Step 2 to the end.
🔍 Visual Examples
Example 1: 3 × 40
- Basic fact: 3 × 4 = 12
- Count the zero: 40 has one zero.
- Attach it: 12 becomes 120.
- Answer: 120
Example 2: 6 × 50
- Basic fact: 6 × 5 = 30
- Count the zero: 50 has one zero.
- Attach it: 30 becomes 300.
- Answer: 300
⚠️ Common Mistakes
Adding Extra Zeros: Don't add a zero to the number you are multiplying by. For 3 × 40, you only use the zero from the 40, you don't change the 3 to 30.
Forgetting the Basic Fact: Always solve the simple multiplication first (3 × 4) before worrying about the zero.
💡 Tips & Tricks
The Zero Trick: When you multiply a whole number by 10, you just "give it a zero." 7 × 10 = 70. For numbers like 20 or 30, multiply by the first digit, then give it the zero.
Place Value Helper: Imagine the numbers on a place value chart. Multiplying by 10 makes every digit "slide" one place to the left, which is why a zero appears in the ones place!
🎯 How to Practice
- Flashcards: Make cards for problems like 4 × 20, 7 × 30, and 9 × 10.
- Real-World Problems: "If one pack has 10 stickers, how many are in 5 packs?"
- Number Patterns: Write down the pattern for 6 × 1, 6 × 10, 6 × 20. See how the numbers change!