Addition

323

Step 1: We know that sum = 712 and one number = 389. We need to find the other number. Step 2: Other number = Sum - Known number = 712 - 389. Step 3: Subtract ones: 2 - 9, we need to borrow. 12 - 9 = 3. Step 4: Subtract tens after borrow: 0 - 8, need to borrow. 10 - 8 = 2. But we borrowed from hundreds too. Step 5: Hundreds: 6 - 3 = 3. So the answer is 323. We can verify: 389 + 323 = 712. Ones: 9+3=12, write 2 carry 1. Tens: 8+2+1=11, write 1 carry 1. Hundreds: 3+3+1=7. Yes! 712 is correct.

617

Step 1: We need to add a 3-digit number 538 and a 2-digit number 79. Write 79 as 079. Step 2: Add ones. 8 + 9 = 17 ones. Write 7 under ones, carry 1 to tens. Step 3: Add tens. 3 + 7 = 10, plus 1 carry = 11 tens. Write 1 under tens, carry 1 to hundreds. Step 4: Add hundreds. 5 + 0 = 5, plus 1 carry = 6 hundreds. Write 6. Final Answer: 617. Students often forget the carry over from tens to hundreds and write 607.

522

Step 1: Priya starts with 245 stamps, gets 178 from friend and 99 from brother. Total = 245 + 178 + 99. Step 2: Add ones. 5 + 8 + 9 = 22 ones. Write 2 under ones, carry 2 to tens. Step 3: Add tens. 4 + 7 + 9 = 20, plus 2 carry = 22 tens. Write 2 under tens, carry 2 to hundreds. Step 4: Add hundreds. 2 + 1 + 0 = 3, plus 2 carry = 5 hundreds. Write 5. Final Answer: 522 stamps. Note: carry over here is 2 not 1 which many students miss.

433

Step 1: We need to find a number X such that 467 + X = 900. Step 2: X = 900 - 467. Step 3: Subtract ones: 0 - 7, borrow needed. 10 - 7 = 3. Step 4: Subtract tens after borrow: 9 - 1(borrowed) - 6 = 2. Wait, 0 becomes 10, we borrowed from tens, so tens is 9-1=9 then 9-6=3. Hundreds: 9-1(borrowed from hundreds)=8, 8-4=4. Hmm, let us verify: 467 + 433. Ones: 7+3=10, write 0 carry 1. Tens: 6+3+1=10, write 0 carry 1. Hundreds: 4+4+1=9. Yes! 467 + 433 = 900. Answer is 433.