Cardinal Math

Three-digit subtraction with regrouping · sheet 30 of 30

Answer key

The answer, and what a wrong answer means.

The sheet
#ProblemAnswerIf they wrote…
1 330 − 327 3 10 zero minus a number is zero13 borrows, but never pays17 smaller from larger or zero minus a number is the number
2 258 − 149 109 111 smaller from larger119 borrows, but never pays
3 908 − 349 559 641 smaller from larger659 borrowing through a zero669 borrows, but never pays
4 418 − 309 109 111 smaller from larger119 borrows, but never pays
5 959 − 754 205 no pattern to catch here
6 503 − 105 398 402 smaller from larger408 borrows, but never pays498 borrowing through a zero
7 911 − 539 372 402 zero minus a number is zero428 smaller from larger432 zero minus a number is the number482 borrows, but never pays
8 304 − 110 194 204 zero minus a number is zero214 smaller from larger or zero minus a number is the number294 borrows, but never pays
9 608 − 299 309 409 borrowing through a zero419 borrows, but never pays491 smaller from larger
10 346 − 256 90 110 smaller from larger190 borrows, but never pays
11 898 − 344 554 no pattern to catch here
12 283 − 192 91 111 smaller from larger191 borrows, but never pays
13 406 − 268 138 238 borrowing through a zero248 borrows, but never pays262 smaller from larger
14 230 − 149 81 119 smaller from larger191 borrows, but never pays90 zero minus a number is zero99 zero minus a number is the number
15 827 − 638 189 211 smaller from larger299 borrows, but never pays
16 907 − 862 45 105 zero minus a number is zero145 borrows, but never pays165 smaller from larger or zero minus a number is the number
17 440 − 252 188 190 zero minus a number is zero192 zero minus a number is the number212 smaller from larger298 borrows, but never pays
18 577 − 482 95 115 smaller from larger195 borrows, but never pays
19 680 − 595 85 115 smaller from larger195 borrows, but never pays90 zero minus a number is zero95 zero minus a number is the number
20 407 − 135 272 302 zero minus a number is zero332 smaller from larger or zero minus a number is the number372 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 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.