Subtracting from 100

🎯 What You'll Learn

You will learn quick strategies for subtracting from 100, which is essential for making change from a ₦100 note.

🏪 Market Story

Funke pays ₦100 for items costing ₦37. She needs to quickly work out her change. Here's a trick: the ones digit and its partner add to 10, the tens digit and its partner add to 9. So for ₦37: ones: 10 − 7 = 3, tens: 9 − 3 = 6. Change: ₦63!

📝 Let's Learn

Quick trick for 100 − any two-digit number:

1. Subtract the ones digit from 10.
2. Subtract the tens digit from 9.
3. Put them together.

Example 1: 100 − 45. Ones: 10 − 5 = 5. Tens: 9 − 4 = 5. Answer: 55.

Example 2: 100 − 82. Ones: 10 − 2 = 8. Tens: 9 − 8 = 1. Answer: 18.

Example 3: 100 − 19. Ones: 10 − 9 = 1. Tens: 9 − 1 = 8. Answer: 81.

Special case: If the ones digit is 0 (like 100 − 30), just think: 10 − 3 = 7, so the answer is 70.

✏️ Practice Questions

1. ₦100 − ₦56 = ?
2. ₦100 − ₦73 = ?
3. Tunde pays ₦100 for food costing ₦68. How much change should he receive?

Click to see answers

1. ₦100 − ₦56 = ₦44. Ones: 10 − 6 = 4. Tens: 9 − 5 = 4.
2. ₦100 − ₦73 = ₦27. Ones: 10 − 3 = 7. Tens: 9 − 7 = 2.
3. ₦100 − ₦68 = ₦32. Ones: 10 − 8 = 2. Tens: 9 − 6 = 3.

💡 Remember

To subtract from 100: ones from 10, tens from 9. This trick lets you calculate change from ₦100 instantly in your head!