Cardinal Math

Three-digit subtraction with regrouping · sheet 28 of 30

Answer key

The answer, and what a wrong answer means.

The sheet
#ProblemAnswerIf they wrote…
1 424 − 192 232 332 borrows, but never pays372 smaller from larger
2 603 − 364 239 339 borrowing through a zero349 borrows, but never pays361 smaller from larger
3 678 − 577 101 no pattern to catch here
4 760 − 389 371 380 zero minus a number is zero389 zero minus a number is the number429 smaller from larger481 borrows, but never pays
5 341 − 315 26 34 smaller from larger36 borrows, but never pays
6 436 − 318 118 122 smaller from larger128 borrows, but never pays
7 606 − 425 181 201 zero minus a number is zero221 smaller from larger or zero minus a number is the number281 borrows, but never pays
8 405 − 107 298 302 smaller from larger308 borrows, but never pays398 borrowing through a zero
9 369 − 181 188 228 smaller from larger288 borrows, but never pays
10 245 − 178 67 133 smaller from larger177 borrows, but never pays
11 978 − 815 163 no pattern to catch here
12 683 − 394 289 311 smaller from larger399 borrows, but never pays
13 605 − 434 171 201 zero minus a number is zero231 smaller from larger or zero minus a number is the number271 borrows, but never pays
14 408 − 349 59 141 smaller from larger159 borrowing through a zero169 borrows, but never pays
15 774 − 579 195 205 borrows, but never pays or smaller from larger
16 507 − 391 116 206 zero minus a number is zero216 borrows, but never pays296 smaller from larger or zero minus a number is the number
17 164 − 137 27 33 smaller from larger37 borrows, but never pays
18 570 − 381 189 190 zero minus a number is zero191 zero minus a number is the number211 smaller from larger299 borrows, but never pays
19 706 − 489 217 317 borrowing through a zero327 borrows, but never pays383 smaller from larger
20 421 − 191 230 330 borrows, but never pays370 smaller from larger

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.