Cardinal Math

Three-digit subtraction with regrouping · sheet 27 of 30

Answer key

The answer, and what a wrong answer means.

The sheet
#ProblemAnswerIf they wrote…
1 864 − 443 421 no pattern to catch here
2 505 − 467 38 138 borrowing through a zero148 borrows, but never pays162 smaller from larger
3 420 − 245 175 180 zero minus a number is zero185 zero minus a number is the number225 smaller from larger285 borrows, but never pays
4 261 − 170 91 111 smaller from larger191 borrows, but never pays
5 587 − 458 129 131 smaller from larger139 borrows, but never pays
6 405 − 254 151 201 zero minus a number is zero251 borrows, but never pays or smaller from larger or zero minus a number is the number
7 380 − 195 185 190 zero minus a number is zero195 zero minus a number is the number215 smaller from larger295 borrows, but never pays
8 715 − 409 306 314 smaller from larger316 borrows, but never pays
9 884 − 394 490 510 smaller from larger590 borrows, but never pays
10 708 − 609 99 101 smaller from larger109 borrows, but never pays199 borrowing through a zero
11 318 − 279 39 109 zero minus a number is zero149 borrows, but never pays161 smaller from larger179 zero minus a number is the number
12 202 − 141 61 101 zero minus a number is zero141 smaller from larger or zero minus a number is the number161 borrows, but never pays
13 508 − 271 237 307 zero minus a number is zero337 borrows, but never pays377 smaller from larger or zero minus a number is the number
14 403 − 377 26 126 borrowing through a zero136 borrows, but never pays174 smaller from larger
15 452 − 182 270 330 smaller from larger370 borrows, but never pays
16 548 − 349 199 201 smaller from larger209 borrows, but never pays
17 540 − 346 194 200 zero minus a number is zero204 borrows, but never pays206 smaller from larger or zero minus a number is the number
18 997 − 777 220 no pattern to catch here
19 700 − 153 547 600 zero minus a number is zero647 borrowing through a zero653 smaller from larger or zero minus a number is the number657 borrows, but never pays
20 562 − 137 425 435 borrows, but never pays or 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 8 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 8 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.