Cardinal Math

Three-digit subtraction with regrouping · sheet 2 of 30

Answer key

The answer, and what a wrong answer means.

The sheet
#ProblemAnswerIf they wrote…
1 287 − 194 93 113 smaller from larger193 borrows, but never pays
2 328 − 159 169 231 smaller from larger279 borrows, but never pays
3 910 − 502 408 410 zero minus a number is zero412 smaller from larger or zero minus a number is the number418 borrows, but never pays
4 683 − 399 284 316 smaller from larger394 borrows, but never pays
5 904 − 317 587 613 smaller from larger687 borrowing through a zero697 borrows, but never pays
6 950 − 189 761 770 zero minus a number is zero779 zero minus a number is the number839 smaller from larger871 borrows, but never pays
7 504 − 435 69 131 smaller from larger169 borrowing through a zero179 borrows, but never pays
8 786 − 583 203 no pattern to catch here
9 783 − 173 610 no pattern to catch here
10 874 − 292 582 622 smaller from larger682 borrows, but never pays
11 407 − 359 48 148 borrowing through a zero152 smaller from larger158 borrows, but never pays
12 852 − 323 529 531 smaller from larger539 borrows, but never pays
13 920 − 272 648 650 zero minus a number is zero652 zero minus a number is the number752 smaller from larger758 borrows, but never pays
14 305 − 293 12 102 zero minus a number is zero112 borrows, but never pays192 smaller from larger or zero minus a number is the number
15 507 − 424 83 103 zero minus a number is zero123 smaller from larger or zero minus a number is the number183 borrows, but never pays
16 506 − 399 107 207 borrowing through a zero217 borrows, but never pays293 smaller from larger
17 767 − 249 518 522 smaller from larger528 borrows, but never pays
18 420 − 335 85 115 smaller from larger195 borrows, but never pays90 zero minus a number is zero95 zero minus a number is the number
19 479 − 292 187 227 smaller from larger287 borrows, but never pays
20 402 − 352 50 100 zero minus a number is zero150 borrows, but never pays or smaller from larger or 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.