Cardinal Math

Three-digit subtraction with regrouping · sheet 21 of 30

Answer key

The answer, and what a wrong answer means.

The sheet
#ProblemAnswerIf they wrote…
1 920 − 744 176 180 zero minus a number is zero184 zero minus a number is the number224 smaller from larger286 borrows, but never pays
2 526 − 437 89 111 smaller from larger199 borrows, but never pays
3 317 − 297 20 120 borrows, but never pays180 smaller from larger
4 306 − 252 54 104 zero minus a number is zero154 borrows, but never pays or smaller from larger or zero minus a number is the number
5 757 − 582 175 235 smaller from larger275 borrows, but never pays
6 880 − 293 587 590 zero minus a number is zero593 zero minus a number is the number613 smaller from larger697 borrows, but never pays
7 706 − 259 447 547 borrowing through a zero553 smaller from larger557 borrows, but never pays
8 509 − 420 89 109 zero minus a number is zero129 smaller from larger or zero minus a number is the number189 borrows, but never pays
9 415 − 126 289 309 zero minus a number is zero311 smaller from larger329 zero minus a number is the number399 borrows, but never pays
10 907 − 150 757 807 zero minus a number is zero857 borrows, but never pays or smaller from larger or zero minus a number is the number
11 406 − 388 18 118 borrowing through a zero128 borrows, but never pays182 smaller from larger
12 978 − 758 220 no pattern to catch here
13 987 − 799 188 212 smaller from larger298 borrows, but never pays
14 596 − 548 48 52 smaller from larger58 borrows, but never pays
15 241 − 181 60 140 smaller from larger160 borrows, but never pays
16 783 − 436 347 353 smaller from larger357 borrows, but never pays
17 301 − 239 62 138 smaller from larger162 borrowing through a zero172 borrows, but never pays
18 114 − 105 9 11 smaller from larger19 borrows, but never pays
19 672 − 321 351 no pattern to catch here
20 604 − 515 89 111 smaller from larger189 borrowing through a zero199 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.