Cardinal Math

Three-digit subtraction with regrouping · sheet 15 of 30

Answer key

The answer, and what a wrong answer means.

The sheet
#ProblemAnswerIf they wrote…
1 303 − 171 132 202 zero minus a number is zero232 borrows, but never pays272 smaller from larger or zero minus a number is the number
2 808 − 649 159 241 smaller from larger259 borrowing through a zero269 borrows, but never pays
3 420 − 141 279 280 zero minus a number is zero281 zero minus a number is the number321 smaller from larger389 borrows, but never pays
4 825 − 748 77 123 smaller from larger187 borrows, but never pays
5 721 − 202 519 521 smaller from larger529 borrows, but never pays
6 668 − 191 477 537 smaller from larger577 borrows, but never pays
7 626 − 367 259 341 smaller from larger369 borrows, but never pays
8 604 − 180 424 504 zero minus a number is zero524 borrows, but never pays584 smaller from larger or zero minus a number is the number
9 740 − 685 55 145 smaller from larger165 borrows, but never pays60 zero minus a number is zero65 zero minus a number is the number
10 972 − 691 281 321 smaller from larger381 borrows, but never pays
11 308 − 199 109 209 borrowing through a zero219 borrows, but never pays291 smaller from larger
12 786 − 370 416 no pattern to catch here
13 906 − 556 350 400 zero minus a number is zero450 borrows, but never pays or smaller from larger or zero minus a number is the number
14 800 − 346 454 500 zero minus a number is zero546 smaller from larger or zero minus a number is the number554 borrowing through a zero564 borrows, but never pays
15 985 − 763 222 no pattern to catch here
16 334 − 215 119 121 smaller from larger129 borrows, but never pays
17 801 − 513 288 312 smaller from larger388 borrowing through a zero398 borrows, but never pays
18 317 − 309 8 12 smaller from larger18 borrows, but never pays
19 517 − 250 267 347 smaller from larger367 borrows, but never pays
20 636 − 579 57 143 smaller from larger167 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.