Mentally Add/Subtract 10 or 100 - 2nd Grade Math

1. What is the result of subtracting $10$ from $489$?

   $479$. Subtracting $10$ decreases the tens digit by $1$.

2. What is the result of subtracting $10$ from $590$?

   $580$. Subtracting $10$ decreases the tens digit by $1$.

3. What is the result of subtracting $10$ from $709$?

   $699$. Subtracting $10$ decreases the tens digit by $1$.

4. What is $563 - 10$?

   $553$. Subtract $1$ from the tens digit: $6 - 1 = 5$.

5. What is the result of subtracting $100$ from $364$?

   $264$. Subtracting $100$ decreases the hundreds digit by $1$.

6. What is $799 + 10$?

   $809$. The $9$ in tens place carries, making $800 + 9 = 809$.

7. What is the result of subtracting $10$ from $600$?

   $590$. Subtracting $10$ from $600$ requires regrouping from the hundreds place.

8. What is the result of adding $10$ to $695$?

   $705$. Adding $10$ to $695$ requires regrouping to the hundreds place.

9. What is $420 - 10$?

   $410$. Subtract $1$ from the tens digit: $2 - 1 = 1$.

10. What is the result of subtracting $10$ from $408$?

    $398$. Subtracting $10$ decreases the tens digit by $1$.

11. What happens to the hundreds digit when you add $100$ to a number from $100$ to $900$?

    The hundreds digit increases by $1$. Adding $100$ changes only the hundreds place value.

12. What is the result of subtracting $100$ from $356$?

    $256$. Subtracting $100$ decreases the hundreds digit by $1$.

13. What is the result of adding $10$ to $408$?

    $418$. Adding $10$ increases the tens digit by $1$.

14. What is $356 + 10$?

    $366$. Add $1$ to the tens digit: $5 + 1 = 6$.

15. What is the result of adding $100$ to $590$?

    $690$. Adding $100$ increases the hundreds digit by $1$.

16. What is the result of adding $10$ to $489$?

    $499$. Adding $10$ increases the tens digit by $1$.

17. What is the result of subtracting $100$ from $800$?

    $700$. Subtracting $100$ decreases the hundreds digit by $1$.

18. What is the result of subtracting $100$ from $695$?

    $595$. Subtracting $100$ decreases the hundreds digit by $1$.

19. What is the result of adding $10$ to $709$?

    $719$. Adding $10$ increases the tens digit by $1$.

20. What is $900 - 100$?

    $800$. Subtract $1$ from the hundreds digit: $9 - 1 = 8$.

21. What is the result of subtracting $10$ from $279$?

    $269$. Subtracting $10$ decreases the tens digit by $1$.

22. What is $835 + 100$?

    $935$. Add $1$ to the hundreds digit: $8 + 1 = 9$.

23. What is the result of subtracting $100$ from $279$?

    $179$. Subtracting $100$ decreases the hundreds digit by $1$.

24. What is the result of adding $100$ to $356$?

    $456$. Adding $100$ increases the hundreds digit by $1$.

25. What happens to the hundreds digit when you subtract $100$ from a number from $100$ to $900$?

    The hundreds digit decreases by $1$. Subtracting $100$ changes only the hundreds place value.

26. What is $690 + 10$?

    $700$. The $9$ in tens place carries, making $700$.

27. What is the result of subtracting $10$ from $800$?

    $790$. Subtracting $10$ from $800$ requires regrouping from hundreds.

28. What happens to the tens digit when you add $10$ to a number from $100$ to $900$?

    The tens digit increases by $1$ (and may cause a carry). Adding $10$ affects the tens place, which may carry to hundreds.

29. What is the result of adding $10$ to $800$?

    $810$. Adding $10$ increases the tens digit by $1$.

30. What is the result of adding $100$ to $408$?

    $508$. Adding $100$ increases the hundreds digit by $1$.

31. What is $700 - 10$?

    $690$. Borrow from hundreds: $10 - 1 = 9$ in tens place.

32. What is the result of adding $100$ to $800$?

    $900$. Adding $100$ increases the hundreds digit by $1$.

33. What is the result of adding $100$ to $364$?

    $464$. Adding $100$ increases the hundreds digit by $1$.

34. What is the result of adding $10$ to $590$?

    $600$. Adding $10$ to $590$ requires regrouping to the hundreds place.

35. What is the result of adding $10$ to $279$?

    $289$. Adding $10$ increases the tens digit by $1$.

36. What happens to the tens digit when you subtract $10$ from a number from $100$ to $900$?

    The tens digit decreases by $1$ (and may require borrowing). Subtracting $10$ affects the tens place, sometimes requiring regrouping.

37. What is the result of adding $10$ to $364$?

    $374$. Adding $10$ increases the tens digit by $1$.

38. What is the result of adding $10$ to $356$?

    $366$. Adding $10$ increases the tens digit by $1$.

39. What is $615 - 100$?

    $515$. Subtract $1$ from the hundreds digit: $6 - 1 = 5$.

40. What is $508 + 100$?

    $608$. Add $1$ to the hundreds digit: $5 + 1 = 6$.

41. What is the result of subtracting $100$ from $408$?

    $308$. Subtracting $100$ decreases the hundreds digit by $1$.

42. What is the result of adding $100$ to $279$?

    $379$. Adding $100$ increases the hundreds digit by $1$.

43. What is the result of subtracting $10$ from $356$?

    $346$. Subtracting $10$ decreases the tens digit by $1$.

44. What is $478 + 10$?

    $488$. Add $1$ to the tens digit: $7 + 1 = 8$.

45. What is the result of subtracting $100$ from $709$?

    $609$. Subtracting $100$ decreases the hundreds digit by $1$.

46. What is the result of subtracting $10$ from $364$?

    $354$. Subtracting $10$ decreases the tens digit by $1$.

47. What is the result of subtracting $100$ from $900$?

    $800$. Subtracting $100$ from $900$ gives the previous hundred.

48. What is the result of subtracting $10$ from $705$?

    $695$. Subtracting $10$ from $705$ requires regrouping from the hundreds place.

49. What is the result of adding $100$ to $709$?

    $809$. Adding $100$ increases the hundreds digit by $1$.

50. What is the result of adding $100$ to $489$?

    $589$. Adding $100$ increases the hundreds digit by $1$.

51. What is $300 - 100$?

    $200$. Subtract $1$ from the hundreds digit: $3 - 1 = 2$.

52. What is $245 + 100$?

    $345$. Add $1$ to the hundreds digit: $2 + 1 = 3$.

53. What is $672 - 100$?

    $572$. Subtract $1$ from the hundreds digit: $6 - 1 = 5$.

54. What is the result of adding $100$ to $695$?

    $795$. Adding $100$ increases the hundreds digit by $1$.

55. What is the result of subtracting $100$ from $590$?

    $490$. Subtracting $100$ decreases the hundreds digit by $1$.

56. What is the result of subtracting $100$ from $489$?

    $389$. Subtracting $100$ decreases the hundreds digit by $1$.

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