Cardinal Math

Three-digit subtraction with regrouping · sheet 12 of 30

Answer key

The answer, and what a wrong answer means.

The sheet
#ProblemAnswerIf they wrote…
1 921 − 156 765 835 smaller from larger875 borrows, but never pays
2 978 − 229 749 751 smaller from larger759 borrows, but never pays
3 906 − 724 182 202 zero minus a number is zero222 smaller from larger or zero minus a number is the number282 borrows, but never pays
4 597 − 486 111 no pattern to catch here
5 508 − 109 399 401 smaller from larger409 borrows, but never pays499 borrowing through a zero
6 331 − 290 41 141 borrows, but never pays161 smaller from larger
7 501 − 248 253 347 smaller from larger353 borrowing through a zero363 borrows, but never pays
8 646 − 288 358 442 smaller from larger468 borrows, but never pays
9 214 − 142 72 132 smaller from larger172 borrows, but never pays
10 807 − 672 135 205 zero minus a number is zero235 borrows, but never pays275 smaller from larger or zero minus a number is the number
11 285 − 209 76 84 smaller from larger86 borrows, but never pays
12 460 − 381 79 121 smaller from larger189 borrows, but never pays80 zero minus a number is zero81 zero minus a number is the number
13 360 − 213 147 150 zero minus a number is zero153 smaller from larger or zero minus a number is the number157 borrows, but never pays
14 744 − 604 140 no pattern to catch here
15 902 − 826 76 124 smaller from larger176 borrowing through a zero186 borrows, but never pays
16 911 − 151 760 840 smaller from larger860 borrows, but never pays
17 934 − 559 375 425 smaller from larger485 borrows, but never pays
18 404 − 110 294 304 zero minus a number is zero314 smaller from larger or zero minus a number is the number394 borrows, but never pays
19 500 − 478 22 100 zero minus a number is zero122 borrowing through a zero132 borrows, but never pays178 smaller from larger or zero minus a number is the number
20 440 − 379 61 139 smaller from larger171 borrows, but never pays70 zero minus a number is zero79 zero minus a number is the number

Reading the wrong answers

One wrong answer is a slip. The same pattern on three or more problems is a rule your child is following, and it has a name and a fix in the guide. Problems marked "no pattern to catch" are the plain ones; a child who gets only those right is telling you something too.

Borrows, but never pays 18 of 20 problems

Adds ten to the ones but leaves the tens alone. Looks like borrowing; the answer is ten too big.

52 − 38 they write 24 it is 14

Smaller from larger 18 of 20 problems

Takes the smaller digit from the bigger one in every column, whichever is on top. Never borrows.

52 − 38 they write 26 it is 14

Zero minus a number is the number 7 of 20 problems

When the top digit is 0, writes the bottom digit as that column's answer.

40 − 27 they write 27 it is 13

Zero minus a number is zero 7 of 20 problems

When the top digit is 0, writes 0 for that column.

40 − 27 they write 20 it is 13

Borrowing through a zero 4 of 20 problems

Turns the 0 into a 9 and gives the ones their ten, but never reduces the column left of the zero.

302 − 167 they write 235 it is 135

Not sure which? The five-minute check picks the problems that tell the patterns apart and names the one it sees.