Cardinal Math

Two-digit subtraction with regrouping · sheet 28 of 30

Answer key

The answer, and what a wrong answer means.

The sheet
#ProblemAnswerIf they wrote…
1 85 − 22 63 no pattern to catch here
2 90 − 47 43 53 borrows, but never pays57 smaller from larger
3 39 − 38 1 no pattern to catch here
4 30 − 16 14 24 borrows, but never pays26 smaller from larger
5 97 − 79 18 22 smaller from larger28 borrows, but never pays
6 92 − 83 9 11 smaller from larger19 borrows, but never pays
7 93 − 35 58 62 smaller from larger68 borrows, but never pays
8 36 − 19 17 23 smaller from larger27 borrows, but never pays
9 75 − 30 45 no pattern to catch here
10 93 − 75 18 22 smaller from larger28 borrows, but never pays
11 94 − 57 37 43 smaller from larger47 borrows, but never pays
12 25 − 17 8 12 smaller from larger18 borrows, but never pays
13 70 − 54 16 24 smaller from larger26 borrows, but never pays
14 70 − 36 34 44 borrows, but never pays46 smaller from larger
15 96 − 89 7 13 smaller from larger17 borrows, but never pays
16 76 − 69 7 13 smaller from larger17 borrows, but never pays
17 70 − 61 9 11 smaller from larger19 borrows, but never pays
18 57 − 27 30 no pattern to catch here
19 16 − 13 3 no pattern to catch here
20 97 − 18 79 81 smaller from larger89 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 15 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 15 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

Not sure which? The five-minute check picks the problems that tell the patterns apart and names the one it sees.