Elementary School Math Quiz: Mentally Add Subtract 10 Or 100
20 questions · exam conditions
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Mentally Add Subtract 10 Or 100Question 1 of 20

What is 905−10905 - 10?

895
905
995
904
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Elementary School Math Quiz

Elementary School Math Quiz: Mentally Add Subtract 10 Or 100

Practice Mentally Add Subtract 10 Or 100 in Elementary School Math with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Mentally Add Subtract 10 Or 100, giving you a quick way to practice the rules, question types, and explanations that matter most for Elementary School Math.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

What is 905−10905 - 10?

  1. 895 (correct answer)
  2. 905
  3. 995
  4. 904
Explanation: The correct answer is 895, because 905−10=895905 - 10 = 895. Choice B (905) repeats the starting number without subtracting anything. Choice C (995) comes from adding 10 instead of subtracting it. Choice D (904) subtracts only 1 from the ones place instead of subtracting 10 from the tens place.

Question 2

Calculate mentally: 430+100430 + 100.

  1. 440
  2. 530 (correct answer)
  3. 330
  4. 431
Explanation: Adding 100 increases the hundreds digit by 1: 430+100=530430+100=530. Choice A adds only 10 instead of 100. Choice C subtracts 100 instead of adding. Choice D adds only 1 instead of 100.

Question 3

Maya has 312 stickers and gets 10 more. How many stickers does she have now?

  1. 302
  2. 322 (correct answer)
  3. 412
  4. 313
Explanation: 312 plus 10 equals 322, since adding 10 increases the tens digit by 1. 302 would result from subtracting 10 instead of adding it. 412 would result from adding 100 instead of 10. 313 would result from adding only 1 instead of 10.

Question 4

Maya has 347347 stickers. She gives away 1010 stickers to her friend and then buys 100100 more stickers. How many stickers does Maya have now?

  1. 437437 stickers (correct answer)
  2. 447447 stickers
  3. 357357 stickers
  4. 247247 stickers
Explanation: Maya starts with 347 stickers, gives away 10, and then buys 100 more, so 347 - 10 + 100 = 437 stickers, making Choice A correct. Choice B is wrong because it adds 10 back in instead of subtracting it first. Choice C is wrong because it only accounts for giving away stickers, not buying more. Choice D is wrong because it subtracts 100 instead of adding it.

Question 5

Emma saves 164164 pennies in January. In February, she spends 1010 pennies on candy. In March, her grandmother gives her 100100 more pennies. What is the total number of pennies Emma has after March?

  1. 254254 pennies total (correct answer)
  2. 274274 pennies total
  3. 5454 pennies total
  4. 264264 pennies total
Explanation: Emma starts with 164 pennies, spends 10 to have 154, then receives 100 more: 154 + 100 = 254 pennies. Choice B adds all three numbers together. Choice C subtracts 100 instead of adding. Choice D makes an error by adding 10 instead of subtracting it initially.

Question 6

What is 639+10639 + 10?

  1. 649 (correct answer)
  2. 739
  3. 629
  4. 639
Explanation: The correct answer is 649, because 639+10=649639 + 10 = 649. Choice B (739) adds 100 instead of 10. Choice C (629) subtracts 10 instead of adding it. Choice D (639) repeats the starting number without adding anything.

Question 7

What number continues the pattern: 420, 520, 620, ?

  1. 621621
  2. 630630
  3. 720720 (correct answer)
  4. 620620
Explanation: The pattern adds 100 each time: 420, 520, 620, 720, so the missing number is 720, making Choice C correct. Choice A is wrong because it only adds 1 instead of continuing the pattern. Choice B is wrong because it only adds 10 instead of 100. Choice D is wrong because it repeats the number already given instead of continuing the pattern.

Question 8

What is 476−100476 - 100?

  1. 366
  2. 376 (correct answer)
  3. 486
  4. 476
Explanation: Subtracting 100 from 476 lowers the hundreds digit by one, giving 376. Choice A, 366, comes from subtracting 110 instead of 100. Choice C, 486, comes from adding 10 rather than subtracting 100. Choice D, 476, is the original number, as if nothing were subtracted.

Question 9

What is 267+100267 + 100?

  1. 367 (correct answer)
  2. 267
  3. 277
  4. 257
Explanation: Adding 100 to 267 increases the hundreds digit by one, giving 367. Choice B, 267, is the original number left unchanged, as if nothing were added. Choice C, 277, comes from adding only 10 instead of 100. Choice D, 257, comes from subtracting 10 rather than adding 100.

Question 10

What is 721−100721 - 100?

  1. 711
  2. 720
  3. 621 (correct answer)
  4. 821
Explanation: 721 minus 100 equals 621, since subtracting 100 decreases the hundreds digit by 1. 711 would result from subtracting only 10 instead of 100. 720 would result from subtracting only 1 instead of 100. 821 would result from adding 100 instead of subtracting.

Question 11

Maya has 287 stickers and gets 10 more. How many stickers does Maya have now?

  1. 297 (correct answer)
  2. 288
  3. 387
  4. 277
Explanation: Maya has 297 stickers, because 287+10=297287 + 10 = 297. Choice B (288) adds the 10 to the ones place instead of the tens place. Choice C (387) adds 100 instead of 10. Choice D (277) subtracts 10 instead of adding it.

Question 12

What is 463+10463 + 10?

  1. 464464
  2. 453453
  3. 473473 (correct answer)
  4. 563563
Explanation: 463 + 10 = 473, so Choice C is correct. Choice A is wrong because it only adds 1 instead of 10. Choice B is wrong because it subtracts instead of adds. Choice D is wrong because it adds 100 instead of 10.

Question 13

What is 390+10390 + 10?

  1. 391
  2. 400 (correct answer)
  3. 490
  4. 380
Explanation: The correct answer is 400, because 390+10=400390 + 10 = 400. Choice A (391) adds the 10 to the ones place instead of the tens place. Choice C (490) adds 100 instead of 10. Choice D (380) subtracts 10 instead of adding it.

Question 14

What is 639−100639 - 100?

  1. 739
  2. 539 (correct answer)
  3. 639
  4. 629
Explanation: 639 minus 100 equals 539, since subtracting 100 decreases the hundreds digit by 1. 739 would result from adding 100 instead of subtracting. 639 is the starting number, before subtracting anything. 629 would result from subtracting only 10 instead of 100.

Question 15

Continue the pattern: 780, 770, 760, ‾\underline{\hspace{2em}}.

  1. 750 (correct answer)
  2. 660
  3. 760
  4. 761
Explanation: This question tests 2nd grade understanding of mentally adding and subtracting 10 or 100 to/from three-digit numbers using place value patterns (CCSS 2.NBT.B.8: Mentally add 10 or 100 to a given number 100-900, and mentally subtract 10 or 100 from a given number 100-900). To mentally add or subtract 10 or 100, understand which place value digit changes: (1) Adding 10 means adding 1 ten, so tens digit increases by 1 (376 + 10: 7 tens becomes 8 tens = 386; ones and hundreds stay same). (2) Subtracting 10 means subtracting 1 ten, so tens digit decreases by 1 (376 - 10: 7 tens becomes 6 tens = 366). (3) Adding 100 means adding 1 hundred, so hundreds digit increases by 1 (376 + 100: 3 hundreds becomes 4 hundreds = 476; tens and ones stay same). (4) Subtracting 100 means subtracting 1 hundred, so hundreds digit decreases by 1 (528 - 100: 5 hundreds becomes 4 hundreds = 428). Describe pattern: Look only at the digit that changes—just add or subtract 1 from that digit, leave other digits alone. This makes calculation easy to do mentally without writing. In this problem, student must continue pattern of subtracting 10: 780, 770, 760,  . To solve mentally, identify operation (-10 each time), identify which digit changes (tens for -10), change that digit by 1 (decrease for subtraction), keep other digits same: 760 - 10 → tens 6→5, answer 750. Choice A is correct because pattern 780, 770, 760 decreases by 10 each time (tens digit down by 1), so next is 750. This correctly identifies and changes only the appropriate place value digit. Choice B represents specific error: subtracted 100 instead of 10, giving 660 instead of 750. This error typically happens when students confuse subtracting 10 with subtracting 100 or don't recognize the pattern of changing tens. To help students: Teach place value explicitly—'Subtracting 10 means subtracting 1 ten. Which place is tens? Middle digit. So middle digit goes down by 1. Hundreds and ones stay same.' Use place value chart: write 760, show subtracting 10 changes only tens: 7 hundreds | 6 tens → 5 tens | 0 ones = 750. Practice with hundreds: 'Subtracting 100 means subtracting 1 hundred. Which place? Leftmost digit. So leftmost digit goes down by 1. Tens and ones stay same.' Show patterns visually: 780, 770, 760, 750—notice only tens digit changes (8→7→6→5), everything else same. Use number line: jump by 10s backward, notice pattern. Connect to skip counting: counting backward by 10s (780, 770, 760...) uses same skill. Practice mental calculation: 'Don't write. Just change one digit in your head.' Teach exceptions: 398 + 10 requires regrouping (9 tens + 1 ten = 10 tens = 1 hundred 0 tens), 302 - 10 requires borrowing (0 tens, borrow from hundreds). Watch for: changing wrong digit, changing wrong amount, confusing ±10 with ±100, not understanding place value, changing multiple digits.

Question 16

What number completes the equation 672+n=682672 + n = 682?

  1. 100
  2. 10 (correct answer)
  3. 12
  4. 682
Explanation: The missing number is 10, because 672+10=682672 + 10 = 682 (the tens digit increases by 1, from 7 to 8). Choice A (100) adds a full hundred instead of a ten. Choice C (12) is close to 10 but doesn't produce the correct sum. Choice D (682) repeats the total instead of finding the missing addend.

Question 17

What number comes next: 900, 800, 700,  ?

  1. 701
  2. 710
  3. 600 (correct answer)
  4. 690
Explanation: The pattern counts down by 100 each time, so after 700 comes 600. 701 mistakenly adds 1 instead of subtracting 100. 710 and 690 both subtract only 10 from 700 instead of subtracting the full 100.

Question 18

When you add 100 to 431, which digit changes?

  1. All digits
  2. Hundreds digit (correct answer)
  3. Ones digit
  4. Tens digit
Explanation: Adding 100 changes only the hundreds digit: 431 becomes 531, since the hundreds digit goes from 4 to 5. Choice A is incorrect because the tens and ones digits stay the same. Choice C is incorrect because the ones digit isn't affected when adding a multiple of 100. Choice D is incorrect because the tens digit also stays the same.

Question 19

What is 805−10805 - 10?

  1. 795 (correct answer)
  2. 705
  3. 815
  4. 805
Explanation: This question tests 2nd grade understanding of mentally adding and subtracting 10 or 100 to/from three-digit numbers using place value patterns (CCSS 2.NBT.B.8: Mentally add 10 or 100 to a given number 100-900, and mentally subtract 10 or 100 from a given number 100-900). To mentally add or subtract 10 or 100, understand which place value digit changes: (1) Adding 10 means adding 1 ten, so tens digit increases by 1 (376+10376 + 10: 77 tens becomes 88 tens = 386386; ones and hundreds stay same). (2) Subtracting 10 means subtracting 1 ten, so tens digit decreases by 1 (376−10376 - 10: 77 tens becomes 66 tens = 366366). (3) Adding 100 means adding 1 hundred, so hundreds digit increases by 1 (376+100376 + 100: 33 hundreds becomes 44 hundreds = 476476; tens and ones stay same). (4) Subtracting 100 means subtracting 1 hundred, so hundreds digit decreases by 1 (528−100528 - 100: 55 hundreds becomes 44 hundreds = 428428). Describe pattern: Look only at the digit that changes—just add or subtract 1 from that digit, leave other digits alone. This makes calculation easy to do mentally without writing. In this problem, student must subtract 10 from 805 mentally. To solve mentally, identify operation (-10), identify which digit changes (tens for -10), change that digit by 1 (decrease for subtraction), keep other digits same: 805−10805 - 10 → tens 0→90 \to 9 (borrowing from hundreds), but since 0 tens, borrow: hundreds 8→78 \to 7, tens 0→90 \to 9 (actually 10−1=910-1=9), ones 5 same, answer 795. Choice A is correct because subtracting 10 from 805 means subtracting 1 from tens digit, but with borrowing (0 tens can't subtract 1, so borrow from hundreds: 8 hundreds become 7, 0 tens become 10, then 10−1=910-1=9 tens), keeping ones (5) same, giving 795. This correctly identifies and changes only the appropriate place value digit with borrowing. Choice B represents specific error: subtracted 100 instead of 10, giving 705 instead of 795. This error typically happens when students confuse subtracting 10 with subtracting 100 or don't understand which place value changes with -10 vs -100. To help students: Teach place value explicitly—'Subtracting 10 means subtracting 1 ten. Which place is tens? Middle digit. So middle digit goes down by 1. Hundreds and ones stay same.' Use place value chart: write 805, show subtracting 10 changes only tens, but borrow: 8 hundreds → 7 hundreds | 0 tens → 9 tens | 5 ones = 795. Practice with hundreds: 'Subtracting 100 means subtracting 1 hundred. Which place? Leftmost digit. So leftmost digit goes down by 1. Tens and ones stay same.' Show patterns visually: 825, 815, 805, 795—notice only tens digit changes (2→1→0→92 \to 1 \to 0 \to 9), with borrowing when needed. Use number line: jump by 10s backward, notice pattern. Connect to skip counting: counting backward by 10s (820,810,800...820, 810, 800...) uses same skill. Practice mental calculation: 'Don't write. Just change one digit in your head.' Teach exceptions: 398+10398 + 10 requires regrouping (99 tens + 11 ten = 1010 tens = 11 hundred 00 tens), 302−10302 - 10 requires borrowing (00 tens, borrow from hundreds). Watch for: changing wrong digit, changing wrong amount, confusing ±10 with ±100, not understanding place value, changing multiple digits.

Question 20

A parking lot had 568568 cars in the morning. During lunch time, 100100 cars left the parking lot. Then 1010 more cars left in the afternoon. How many cars are in the parking lot now?

  1. 678678 cars remaining
  2. 558558 cars remaining
  3. 458458 cars remaining (correct answer)
  4. 468468 cars remaining
Explanation: Start with 568 cars. Subtract 100: 568 - 100 = 468. Then subtract 10: 468 - 10 = 458. Choice A adds both numbers instead of subtracting. Choice B only subtracts 10. Choice D only subtracts 100.