Cardinal Math

Three-digit subtraction with regrouping · sheet 8 of 30

Answer key

The answer, and what a wrong answer means.

The sheet
#ProblemAnswerIf they wrote…
1 735 − 668 67 133 smaller from larger177 borrows, but never pays
2 404 − 314 90 100 zero minus a number is zero110 smaller from larger or zero minus a number is the number190 borrows, but never pays
3 520 − 186 334 340 zero minus a number is zero346 zero minus a number is the number444 borrows, but never pays466 smaller from larger
4 626 − 317 309 311 smaller from larger319 borrows, but never pays
5 595 − 568 27 33 smaller from larger37 borrows, but never pays
6 251 − 191 60 140 smaller from larger160 borrows, but never pays
7 887 − 687 200 no pattern to catch here
8 899 − 278 621 no pattern to catch here
9 872 − 775 97 103 smaller from larger107 borrows, but never pays
10 701 − 606 95 105 borrows, but never pays or smaller from larger195 borrowing through a zero
11 422 − 325 97 103 smaller from larger107 borrows, but never pays
12 605 − 507 98 102 smaller from larger108 borrows, but never pays198 borrowing through a zero
13 602 − 438 164 236 smaller from larger264 borrowing through a zero274 borrows, but never pays
14 407 − 148 259 341 smaller from larger359 borrowing through a zero369 borrows, but never pays
15 225 − 207 18 22 smaller from larger28 borrows, but never pays
16 904 − 744 160 200 zero minus a number is zero240 smaller from larger or zero minus a number is the number260 borrows, but never pays
17 601 − 411 190 200 zero minus a number is zero210 smaller from larger or zero minus a number is the number290 borrows, but never pays
18 720 − 494 226 230 zero minus a number is zero234 zero minus a number is the number336 borrows, but never pays374 smaller from larger
19 815 − 451 364 444 smaller from larger464 borrows, but never pays
20 553 − 393 160 240 smaller from larger260 borrows, but never pays

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.