Mental Math Worksheets

Pick one mental strategy, press Make a new sheet, and print problems written across with nowhere to do column work.

Sheet type

Problems

Answer key

20 problems. Plus or minus 10 or 100, one digit changes. Sheet 1UDRH9, with its answer key.

Plus or minus 10 or 100, one digit changes

Name Date Score / 20

Each problem adds or takes away 10 or 100. Read the sign and the number after it, then work it out in your head.

1.569 + 10 = ________
2.868 + 10 = ________
3.729 − 10 = ________
4.447 + 10 = ________
5.217 + 10 = ________
6.415 − 10 = ________
7.899 − 10 = ________
8.315 − 10 = ________
9.718 + 100 = ________
10.836 + 100 = ________
11.243 + 10 = ________
12.255 − 100 = ________
13.849 − 100 = ________
14.229 + 100 = ________
15.332 + 100 = ________
16.640 + 10 = ________
17.654 − 10 = ________
18.438 − 10 = ________
19.521 − 10 = ________
20.430 − 100 = ________

Sheet 1UDRH9 · Made at homeroomtools.com

Answer key. Plus or minus 10 or 100, one digit changes

1.569 + 10 = 579
2.868 + 10 = 878
3.729 − 10 = 719
4.447 + 10 = 457
5.217 + 10 = 227
6.415 − 10 = 405
7.899 − 10 = 889
8.315 − 10 = 305
9.718 + 100 = 818
10.836 + 100 = 936
11.243 + 10 = 253
12.255 − 100 = 155
13.849 − 100 = 749
14.229 + 100 = 329
15.332 + 100 = 432
16.640 + 10 = 650
17.654 − 10 = 644
18.438 − 10 = 428
19.521 − 10 = 511
20.430 − 100 = 330

Sheet 1UDRH9 · Made at homeroomtools.com

Next step See 10 more and 10 less on a hundreds chart Print grade 2 place value sheets, to 999

How it works

Make mental math worksheets that practice one strategy at a time, from make ten to times 5 by halving. Problems run across with no working space, and the numbers are chosen to suit the move. The key follows the sheet.

Read the full guide

Why the problems are written across

Written across, 46 + 37 gives no columns to fill in. The move the sheet is named for works on whole numbers instead: 46, then 76, then 83. Each strategy sheet draws only numbers the move suits. On the add 9 sheet no first number ends in 0 or 1, where the shortcut would save nothing.

From make ten to quick multiplying

The groups run from Make ten and bridge through ten, for grades 1 and 2, to Multiply and divide in your head, where Times 5 as half of times 10: 5 × 18 sits. Teach one move, print its sheet, then set Addition facts to 20, no strategy named from the last group and see who uses the move unprompted.

Read a sheet aloud as a warm-up: say each problem once, and pupils write only the answer.
Print the add 9 sheet and the subtract 9 sheet a few days apart: one takes 1 back, the other puts 1 back.
Before Same difference: 83 − 49 becomes 84 − 50, slide both numbers up by 1 on a number line on the board.

Questions and answers

What are mental math strategies?

They are ways of turning a problem into an easier one to hold in your head. Three from this page: make ten (8 + 6 becomes 10 + 4), adding 9 as plus 10, minus 1, and times 5 as half of times 10.

How do you add 9 in your head?

Add 10, then take 1 back: 46 + 9 is 46 + 10 − 1 = 55. To subtract 9, take 10 away and put 1 back: 63 − 9 = 54. There is a sheet for each move.

Which grades are these sheets for?

Grades 1 to 4. Make ten and 10 more or less suit grade 1. The moves for 2-digit addition and subtraction suit grades 2 and 3. The multiplication group, such as Split the 2-digit factor: 7 × 13, suits grades 3 and 4.

All 33 sheet types

Make ten and bridge through ten 5

Bridge back through a ten: 52 − 7 52 − 7 = 45. Take away 2 to reach 50, then take away the other 5. The ones digit of the first number is always smaller than the number taken away, so each problem drops into the ten below.
Bridge the next ten: 47 + 8 47 + 8 = 55. Use 3 of the 8 to reach 50, then add the 5 that is left. The ones always add to 10 or more, so every problem reaches or crosses the next ten, and nothing is written down on the way.
Make ten, then add the rest: 8 + 6 8 + 6 = 14. Take 2 from the 6 to fill the 8 up to 10, then add the 4 that is left. Every first number is 7, 8 or 9 and every sum passes 10, so the same move works on every problem. Only 20 such facts exist, and none prints twice.

Show all 33 sheet types (30 more)

Make ten and bridge through ten, continued

Subtract through ten: 13 − 4 13 − 4 = 9. Take away 3 to land on 10, then take away the last 1. The number taken is always more than the ones digit of the teen number, so every problem has to pass through 10 on the way down.
Think addition to subtract: 12 − 8 12 − 8 = 4, because 8 + 4 = 12. Every problem takes away 6 or more, where counting back is slow and easy to lose track of. Pupils ask what goes with the smaller number to make the larger one.

Doubles 1

Double a 2-digit number in parts: 36 + 36 Each double is printed as a sum, so 36 + 36 = 72. Double 30 is 60, double 6 is 12, and 60 + 12 = 72. Numbers run from 12 to 49. Where the ones are 5 or more, as in 36, the two parts have to be joined across a ten.

Add and subtract 9, 99 and other near-round numbers 6

Add 9 to a 2-digit number: + 10, − 1 46 + 9 = 55. Add 10 to reach 56, then take 1 back. The first number runs from 22 to 89 and never ends in 0 or 1, so counting on in ones is always the slow way and the shortcut pays off.
Add 19, 29 or 39: add the ten, take 1 back 45 + 29 = 74. Add 30 to reach 75, then take 1 back. The second number is always 19, 29 or 39 and sums stay under 100. A pupil who can add whole tens can do every problem here without writing a column.
Add 99 to a 3-digit number: + 100, − 1 346 + 99 = 445. Add 100 to reach 446, then take 1 back. First numbers run from 111 to 899 and have no zero in them, so the hundreds digit goes up by 1 and the last two digits drop by 1 every time.
Same difference: 83 − 49 becomes 84 − 50 83 − 49 = 34. Add 1 to both numbers and the problem becomes 84 − 50, which is also 34. The gap between two numbers does not change when both move by the same amount. The number taken away always ends in 8 or 9.
Subtract 9 from a 2-digit number: − 10, + 1 63 − 9 = 54. Take away 10 to reach 53, then put 1 back, because 10 was 1 too many. The adjustment runs the other way from adding 9, so this sheet holds only subtraction and pupils can settle the rule first.
Subtract 99 from a 3-digit number: − 100, + 1 520 − 99 = 421. Take away 100 to reach 420, then put 1 back. First numbers run from 200 to 888 and have no 9 in them, so the hundreds digit drops by 1 and the last two digits rise by 1 every time.

10 or 100 more and less, whole tens and hundreds 6

10 more and 10 less across a hundred: 395 + 10 395 + 10 = 405 and 604 − 10 = 594. Every problem carries into the next hundred or borrows from the one above, so two digits change at once. Set it after the one-digit sheet, when plus 10 has started to feel automatic.
10 more or 10 less than a 2-digit number 57 + 10 = 67 and 57 − 10 = 47. Only the tens digit moves, and the ones digit stays put. Numbers run from 11 to 89 and the sign changes from problem to problem, so pupils must read each one before they answer.
Add whole tens to a 2-digit number: 34 + 50 34 + 50 = 84. Three tens and five tens make eight tens, and the 4 ones are untouched. The second number is always a whole ten from 10 to 60 and sums stay under 100, so nothing carries.
Plus or minus 10 or 100, one digit changes 638 + 100 = 738 and 638 − 10 = 628. One digit changes and the other two stay. With four possible moves, plus or minus 10 or 100, pupils have to decide which place is changing before they write anything.
Rows of 100 less, 10 less, 10 more, 100 more Around 452 the row reads 352, 442, then 462 and 552, because 452 − 100 = 352 and 452 + 10 = 462. Filling four boxes for one number lets pupils compare the moves side by side. Each sheet has 8 rows.
Subtract whole tens from whole tens: 80 − 30 80 − 30 = 50, because 8 tens take away 3 tens leaves 5 tens. Every number is a whole ten from 10 to 90, so each problem is a basic fact with a zero on the end. Say the fact first: 8 − 3 = 5.

Friendly pairs and 2-digit sums 3

Add tens, then ones: 34 + 25 34 + 25 = 59. Add the tens, 30 + 20 = 50, then the ones, 4 + 5 = 9. The ones never add to 10 or more, so this is the first 2-digit sheet to try without columns. Written across, the numbers cannot be lined up.
Count up when the numbers are close: 62 − 58 62 − 58 = 4. From 58 it is 2 up to 60 and 2 more to 62. The two numbers are never more than 9 apart and are always in different tens, so counting up beats taking 58 away.
Keep the first number whole and jump on: 46 + 37 46 + 37 = 83. Keep 46 whole, jump 30 to 76, then 7 more to 83. The ones always add to 10 or more here, where splitting both numbers leaves three part answers to hold. Jumping on leaves one running total.

Multiply and divide in your head 8

Double, then double again for × 4: 4 × 16 4 × 16 = 64. Double 16 is 32, and double 32 is 64. The other factor runs from 6 to 25. One more doubling gives × 8, which is why the 2, 4 and 8 times tables are worth learning as a set.
Halve one factor, double the other: 16 × 5 16 × 5 = 80. Halve the 16 and double the 5, and the problem becomes 8 × 10. One factor is always even, from 12 to 28, and the other is 5, 15 or 25, so the doubled factor is 10, 30 or 50.
Halve, then halve again for ÷ 4: 96 ÷ 4 96 ÷ 4 = 24. Half of 96 is 48, and half of 48 is 24. Every number divided is a multiple of 4 from 28 to 100, so both halvings come out whole. It is the double, double sheet run backward.
Split the 2-digit factor: 7 × 13 7 × 13 = 91. Seven 10s are 70, seven 3s are 21, and 70 + 21 = 91. The 2-digit factor stays between 11 and 19, so the first part is always the other factor with a zero on the end.
Times 5 as half of times 10: 5 × 18 5 × 18 = 90. Ten 18s are 180, and half of 180 is 90. The other factor is always even, from 12 to 48, so the halving comes out to a whole ten and pupils can check that every answer ends in 0.
Times 9 as times 10 minus one group: 9 × 7 9 × 7 = 63. Ten 7s are 70, and one 7 fewer is 63. The second factor runs from 3 to 12, so 9 × 12 = 108 is there too: ten 12s are 120, and one 12 fewer is 108.
Times 10 and times 100: 34 × 10 34 × 10 = 340 and 34 × 100 = 3,400. Each digit moves one place to the left for every zero in the multiplier. Saying that, and not that a zero gets added, still holds when decimals arrive in later grades.
Whole tens times 1 digit: 40 × 6 40 × 6 = 240. Work out 4 × 6 = 24, then make it ten times bigger. The whole ten runs from 10 to 90 and the other factor from 2 to 9. Products such as 50 × 4 = 200 end in two zeros.

Mixed pages and estimates 4

Addition facts to 20, no strategy named A plain page of 20 facts such as 7 + 8 = 15, written across, with no hint about which move to use. Set it after a run of strategy sheets and ask three pupils how they got one answer.
Estimate first, then find the exact answer For 38 + 43, round to 40 + 40 = 80, then find the exact 38 + 43 = 81. An estimate made first tells a pupil whether the exact answer is believable. Each sheet has 8 problems, 4 sums and 4 differences.
Subtraction facts within 20, no strategy named A plain page of 20 facts such as 15 − 7 = 8, written across. Pupils choose between counting back, going through 10 and thinking of the addition. No answer on the sheet is 0, and no problem takes away 0.
Sums to 100 written across, no columns Twelve sums such as 46 + 37 = 83, written across so the digits cannot be lined up in columns. Some need a jump across a ten and some do not, and pupils pick their own move. The answer key prints after the sheet.

How this list was compiled: Own work. Each sheet type practices one mental strategy, and every worked example was checked twice by script. Standards codes were read in the full texts on 2026-09-19: Common Core State Standards for Mathematics (California Department of Education copy), https://www.cde.ca.gov/be/st/ss/documents/ccssmathstandardaug2013.pdf, and Texas Essential Knowledge and Skills, 19 TAC chapter 111 subchapter A, https://tea.texas.gov/sites/default/files/ch111a.pdf. Licence: own work