Use compensation to add - up to two digits
Let's make it friendly! 😊 Compensation is a clever trick where you change one number to make it easier to add (like a number ending in 0), and then you adjust the answer at the end. 🧠
Concept
Compensation is a mental math strategy that helps you add numbers quickly by adjusting them to make them 'friendlier'. The goal is usually to make one of the numbers a multiple of 10. **How it Works (The Give and Take):** Let's solve **28 + 45**. 1. **Make one number friendly:** 28 is very close to 30. Let's give it 2 to make it 30. (28 + 2 = 30). 2. **Do the easy addition:** Now the problem is 30 + 45. That's much easier! 30 + 45 = 75. 3. **Compensate (adjust):** Because we *added* 2 at the start to make the problem easier, we have to *take away* 2 from the answer to make it fair. 4. 75 - 2 = 73. So, **28 + 45 = 73**. **You can also do it the other way (take and give):** Let's solve **39 + 54**. 1. **Make one number friendly:** 39 is close to 40. Add 1 to it. 2. **Adjust the other number:** Since you gave 1 to the 39, you must take 1 away from the 54 to keep it balanced. 54 - 1 = 53. 3. **Do the easy addition:** Now the problem is 40 + 53. That's 93. **Key Idea:** Whatever you do to one number to make it friendly, you must do the opposite to the final answer (or the other number) to balance it out. It's like borrowing and paying back.
Try it
Practice: Use compensation to add - up to two digits.