Cardinal Math

Three-digit subtraction with regrouping · sheet 6 of 30

Answer key

The answer, and what a wrong answer means.

The sheet
#ProblemAnswerIf they wrote…
1 597 − 539 58 62 smaller from larger68 borrows, but never pays
2 570 − 387 183 190 zero minus a number is zero197 zero minus a number is the number217 smaller from larger293 borrows, but never pays
3 892 − 529 363 373 borrows, but never pays377 smaller from larger
4 787 − 389 398 402 smaller from larger408 borrows, but never pays
5 308 − 149 159 241 smaller from larger259 borrowing through a zero269 borrows, but never pays
6 631 − 292 339 449 borrows, but never pays461 smaller from larger
7 779 − 383 396 416 smaller from larger496 borrows, but never pays
8 887 − 253 634 no pattern to catch here
9 400 − 152 248 300 zero minus a number is zero348 borrowing through a zero352 smaller from larger or zero minus a number is the number358 borrows, but never pays
10 703 − 462 241 301 zero minus a number is zero341 borrows, but never pays361 smaller from larger or zero minus a number is the number
11 723 − 618 105 115 borrows, but never pays or smaller from larger
12 770 − 372 398 400 zero minus a number is zero402 smaller from larger or zero minus a number is the number408 borrows, but never pays
13 905 − 169 736 836 borrowing through a zero846 borrows, but never pays864 smaller from larger
14 302 − 221 81 101 zero minus a number is zero121 smaller from larger or zero minus a number is the number181 borrows, but never pays
15 930 − 764 166 170 zero minus a number is zero174 zero minus a number is the number234 smaller from larger276 borrows, but never pays
16 855 − 180 675 735 smaller from larger775 borrows, but never pays
17 400 − 243 157 200 zero minus a number is zero243 smaller from larger or zero minus a number is the number257 borrowing through a zero267 borrows, but never pays
18 624 − 592 32 132 borrows, but never pays172 smaller from larger
19 302 − 161 141 201 zero minus a number is zero241 borrows, but never pays261 smaller from larger or zero minus a number is the number
20 717 − 612 105 no pattern to catch here

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 8 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 8 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.