Cardinal Math

Three-digit subtraction with regrouping · sheet 20 of 30

Answer key

The answer, and what a wrong answer means.

The sheet
#ProblemAnswerIf they wrote…
1 602 − 398 204 304 borrowing through a zero314 borrows, but never pays396 smaller from larger
2 682 − 290 392 412 smaller from larger492 borrows, but never pays
3 773 − 478 295 305 borrows, but never pays or smaller from larger
4 959 − 227 732 no pattern to catch here
5 807 − 333 474 504 zero minus a number is zero534 smaller from larger or zero minus a number is the number574 borrows, but never pays
6 506 − 119 387 413 smaller from larger487 borrowing through a zero497 borrows, but never pays
7 706 − 489 217 317 borrowing through a zero327 borrows, but never pays383 smaller from larger
8 623 − 317 306 314 smaller from larger316 borrows, but never pays
9 321 − 308 13 23 borrows, but never pays27 smaller from larger
10 850 − 581 269 270 zero minus a number is zero271 zero minus a number is the number331 smaller from larger379 borrows, but never pays
11 901 − 550 351 401 zero minus a number is zero451 borrows, but never pays or smaller from larger or zero minus a number is the number
12 943 − 245 698 702 smaller from larger708 borrows, but never pays
13 570 − 399 171 180 zero minus a number is zero189 zero minus a number is the number229 smaller from larger281 borrows, but never pays
14 402 − 247 155 245 smaller from larger255 borrowing through a zero265 borrows, but never pays
15 657 − 434 223 no pattern to catch here
16 831 − 481 350 450 borrows, but never pays or smaller from larger
17 776 − 578 198 202 smaller from larger208 borrows, but never pays
18 425 − 418 7 13 smaller from larger17 borrows, but never pays
19 608 − 574 34 104 zero minus a number is zero134 borrows, but never pays174 smaller from larger or zero minus a number is the number
20 347 − 186 161 241 smaller from larger261 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.