Cardinal Math

Three-digit subtraction with regrouping · sheet 10 of 30

Answer key

The answer, and what a wrong answer means.

The sheet
#ProblemAnswerIf they wrote…
1 903 − 380 523 603 zero minus a number is zero623 borrows, but never pays683 smaller from larger or zero minus a number is the number
2 270 − 187 83 117 smaller from larger193 borrows, but never pays90 zero minus a number is zero97 zero minus a number is the number
3 931 − 241 690 710 smaller from larger790 borrows, but never pays
4 850 − 282 568 570 zero minus a number is zero572 zero minus a number is the number632 smaller from larger678 borrows, but never pays
5 572 − 417 155 165 borrows, but never pays or smaller from larger
6 402 − 149 253 347 smaller from larger353 borrowing through a zero363 borrows, but never pays
7 615 − 106 509 511 smaller from larger519 borrows, but never pays
8 306 − 185 121 201 zero minus a number is zero221 borrows, but never pays281 smaller from larger or zero minus a number is the number
9 501 − 369 132 232 borrowing through a zero242 borrows, but never pays268 smaller from larger
10 721 − 460 261 341 smaller from larger361 borrows, but never pays
11 679 − 567 112 no pattern to catch here
12 784 − 692 92 112 smaller from larger192 borrows, but never pays
13 977 − 188 789 811 smaller from larger899 borrows, but never pays
14 987 − 288 699 701 smaller from larger709 borrows, but never pays
15 207 − 189 18 118 borrowing through a zero128 borrows, but never pays182 smaller from larger
16 401 − 311 90 100 zero minus a number is zero110 smaller from larger or zero minus a number is the number190 borrows, but never pays
17 250 − 193 57 143 smaller from larger167 borrows, but never pays60 zero minus a number is zero63 zero minus a number is the number
18 761 − 134 627 633 smaller from larger637 borrows, but never pays
19 925 − 713 212 no pattern to catch here
20 408 − 269 139 239 borrowing through a zero249 borrows, but never pays261 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 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.