Cardinal Math

Three-digit subtraction with regrouping · sheet 17 of 30

Answer key

The answer, and what a wrong answer means.

The sheet
#ProblemAnswerIf they wrote…
1 505 − 480 25 105 zero minus a number is zero125 borrows, but never pays185 smaller from larger or zero minus a number is the number
2 203 − 189 14 114 borrowing through a zero124 borrows, but never pays186 smaller from larger
3 480 − 192 288 290 zero minus a number is zero292 zero minus a number is the number312 smaller from larger398 borrows, but never pays
4 875 − 378 497 503 smaller from larger507 borrows, but never pays
5 361 − 281 80 120 smaller from larger180 borrows, but never pays
6 407 − 150 257 307 zero minus a number is zero357 borrows, but never pays or smaller from larger or zero minus a number is the number
7 595 − 433 162 no pattern to catch here
8 981 − 667 314 324 borrows, but never pays326 smaller from larger
9 507 − 128 379 421 smaller from larger479 borrowing through a zero489 borrows, but never pays
10 494 − 166 328 332 smaller from larger338 borrows, but never pays
11 673 − 388 285 315 smaller from larger395 borrows, but never pays
12 650 − 286 364 370 zero minus a number is zero376 zero minus a number is the number436 smaller from larger474 borrows, but never pays
13 752 − 462 290 310 smaller from larger390 borrows, but never pays
14 501 − 202 299 301 smaller from larger309 borrows, but never pays399 borrowing through a zero
15 408 − 174 234 304 zero minus a number is zero334 borrows, but never pays374 smaller from larger or zero minus a number is the number
16 520 − 374 146 150 zero minus a number is zero154 zero minus a number is the number254 smaller from larger256 borrows, but never pays
17 244 − 207 37 43 smaller from larger47 borrows, but never pays
18 376 − 284 92 112 smaller from larger192 borrows, but never pays
19 788 − 287 501 no pattern to catch here
20 705 − 456 249 349 borrowing through a zero351 smaller from larger359 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 6 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 6 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.