What is the friendly number strategy for subtraction?

📚 What is the Friendly Number Strategy for Subtraction?

The friendly number strategy is a mental math technique used to simplify subtraction problems by changing one of the numbers to a more 'friendly' number, usually a multiple of 10 or 100. This makes the subtraction easier to perform mentally. It involves adjusting the other number accordingly to maintain the correct difference. Think of it like making subtraction less scary! 😃

📜 History and Background

While the exact origin is difficult to pinpoint, the friendly number strategy stems from a broader understanding of number sense and mental math techniques. It's been used by educators and mathematicians for decades to help students develop a stronger understanding of number relationships and improve their calculation skills. The goal is to move away from rigid algorithms and towards more flexible thinking about numbers.

🔑 Key Principles

• 🎯 Identify a Number to Adjust: Look at the numbers in the subtraction problem and decide which one is closest to a 'friendly' number (like 10, 20, 100, etc.). Usually, you'll adjust the number being subtracted (the subtrahend).
• ➕ Add or Subtract to Make it Friendly: Add or subtract a small amount to the chosen number to make it a friendly number. For example, if you have 47, you might add 3 to make it 50.
• ⚖️ Adjust the Other Number: Because you changed one number, you need to adjust the other number (the minuend) by the same amount to keep the difference the same. If you added to the number being subtracted, you also add to the number you are subtracting from. If you subtracted, you subtract.
• ➗ Perform the Simplified Subtraction: Subtract the friendly number from the adjusted minuend. This should be easier to do mentally.

➕ Real-World Examples

Let's look at some examples to see how it works:

Example 1: 92 - 47

1. We want to make 47 a friendly number. It's close to 50.
2. Add 3 to 47 to get 50.
3. Add 3 to 92 (the other number) to get 95.
4. Now we have 95 - 50, which is much easier to do mentally: 95 - 50 = 45

Example 2: 156 - 89

1. We want to make 89 a friendly number. It's close to 90.
2. Add 1 to 89 to get 90.
3. Add 1 to 156 to get 157.
4. Now we have 157 - 90, which is easier to subtract: 157 - 90 = 67

Example 3: 234 - 98

1. We want to make 98 a friendly number. It's close to 100.
2. Add 2 to 98 to get 100.
3. Add 2 to 234 to get 236.
4. Now we have 236 - 100, which is a breeze: 236 - 100 = 136

🧮 Practice Quiz

Try these subtraction problems using the friendly number strategy:

1. 63 - 28
2. 125 - 57
3. 342 - 199
4. 81 - 36
5. 278 - 69
6. 455 - 202
7. 96 - 48

✅ Conclusion

The friendly number strategy is a powerful tool for making subtraction easier, especially for mental math. By converting numbers into friendlier forms, you can simplify the calculations and boost your confidence in math. Give it a try and see how it works for you!