Cardinal Math

Three-digit subtraction with regrouping · sheet 29 of 30

Answer key

The answer, and what a wrong answer means.

The sheet
#ProblemAnswerIf they wrote…
1 949 − 358 591 611 smaller from larger691 borrows, but never pays
2 320 − 176 144 150 zero minus a number is zero156 zero minus a number is the number254 borrows, but never pays256 smaller from larger
3 607 − 549 58 142 smaller from larger158 borrowing through a zero168 borrows, but never pays
4 604 − 316 288 312 smaller from larger388 borrowing through a zero398 borrows, but never pays
5 732 − 490 242 342 borrows, but never pays362 smaller from larger
6 963 − 802 161 no pattern to catch here
7 315 − 208 107 113 smaller from larger117 borrows, but never pays
8 498 − 361 137 no pattern to catch here
9 306 − 246 60 100 zero minus a number is zero140 smaller from larger or zero minus a number is the number160 borrows, but never pays
10 607 − 214 393 403 zero minus a number is zero413 smaller from larger or zero minus a number is the number493 borrows, but never pays
11 285 − 137 148 152 smaller from larger158 borrows, but never pays
12 200 − 175 25 100 zero minus a number is zero125 borrowing through a zero135 borrows, but never pays175 smaller from larger or zero minus a number is the number
13 502 − 452 50 100 zero minus a number is zero150 borrows, but never pays or smaller from larger or zero minus a number is the number
14 702 − 529 173 227 smaller from larger273 borrowing through a zero283 borrows, but never pays
15 438 − 369 69 131 smaller from larger179 borrows, but never pays
16 386 − 288 98 102 smaller from larger108 borrows, but never pays
17 428 − 258 170 230 smaller from larger270 borrows, but never pays
18 320 − 313 7 10 zero minus a number is zero13 smaller from larger or zero minus a number is the number17 borrows, but never pays
19 870 − 294 576 580 zero minus a number is zero584 zero minus a number is the number624 smaller from larger686 borrows, but never pays
20 948 − 159 789 811 smaller from larger899 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 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.