Cardinal Math

Three-digit subtraction with regrouping · sheet 7 of 30

Answer key

The answer, and what a wrong answer means.

The sheet
#ProblemAnswerIf they wrote…
1 707 − 476 231 301 zero minus a number is zero331 borrows, but never pays371 smaller from larger or zero minus a number is the number
2 658 − 273 385 425 smaller from larger485 borrows, but never pays
3 703 − 184 519 619 borrowing through a zero629 borrows, but never pays681 smaller from larger
4 306 − 248 58 142 smaller from larger158 borrowing through a zero168 borrows, but never pays
5 851 − 167 684 716 smaller from larger794 borrows, but never pays
6 804 − 349 455 545 smaller from larger555 borrowing through a zero565 borrows, but never pays
7 698 − 179 519 521 smaller from larger529 borrows, but never pays
8 956 − 465 491 511 smaller from larger591 borrows, but never pays
9 812 − 682 130 230 borrows, but never pays270 smaller from larger
10 847 − 600 247 no pattern to catch here
11 137 − 119 18 22 smaller from larger28 borrows, but never pays
12 867 − 216 651 no pattern to catch here
13 956 − 868 88 112 smaller from larger198 borrows, but never pays
14 502 − 150 352 402 zero minus a number is zero452 borrows, but never pays or smaller from larger or zero minus a number is the number
15 265 − 247 18 22 smaller from larger28 borrows, but never pays
16 305 − 225 80 100 zero minus a number is zero120 smaller from larger or zero minus a number is the number180 borrows, but never pays
17 370 − 182 188 190 zero minus a number is zero192 zero minus a number is the number212 smaller from larger298 borrows, but never pays
18 544 − 357 187 213 smaller from larger297 borrows, but never pays
19 808 − 139 669 731 smaller from larger769 borrowing through a zero779 borrows, but never pays
20 410 − 274 136 140 zero minus a number is zero144 zero minus a number is the number246 borrows, but never pays264 smaller from larger

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 5 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 5 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.