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Homeschool math, Grade 2, subtracting two-digit numbers

Why does my child borrow but forget to cross out the tens?

52 minus 38 answered 24 in pencil: the ones were borrowed for, but the tens were not reduced.

For example: 52 − 38 = 24

The right answer is 14. Your child wrote 24 because they traded a ten to make 12 − 8 in the ones place, but then they left the tens as 5 instead of 4. Lots of kids do this. It's fixable, and you can start tonight. In LOOP we call it "Forgot to carry/borrow (taking away)."

Your child isn't being careless. They know the trade. They just forgot the other half of it: once you take a ten away, the tens digit has to go down by one.

What they wrote52− 3824
The right answer52− 3814
Here is what happened. They saw a 2 over an 8 and borrowed correctly, so 12 − 8 = 4. But they never crossed out the 5, so in the tens they did 5 − 3 = 2. The answer came out 24.

Here is the right way. 52 is 5 tens and 2 ones. Trade 1 ten for 10 ones, and you have 4 tens and 12 ones. Now 12 − 8 = 4 and 5 4 − 3 = 1, so the answer is 14. Teachers call the trade "borrowing." The crossing out is the part to check.

Is it this, or something else?

Before you fix anything, look at what they actually wrote.

24Borrowed for the ones but left the tens as they were. This is the page you're on.
26Took the smaller digit from the bigger one. They did 8 − 2 in the ones instead of borrowing.
13 or 15Their method is fine; one fact slipped. Check which fact: 12 − 8 is the usual one.

One wrong answer might just be a slip. If the same thing shows up again and again, it isn't. The sheet below will show you whether this is a pattern.

Free printable: 12 problems

Two of these (58−23 and 97−45) need no borrowing, so they are your check. If those two come back right and the other ten are all exactly 10 too big, this is probably the mistake. Check the key below for the exact wrong answers.

It prints on its own page.

Answer key

1. 14, 2. 34, 3. 27, 4. 35, 5. 37, 6. 27, 7. 56, 8. 52, 9. 38, 10. 27, 11. 29, 12. 23.

A child making this mistake will write 24, 44, 37, 47, 37, 66, 48, 37, 39, 33 for problems 1, 2, 3, 5, 6, 7, 9, 10, 11, 12. Every one is exactly 10 bigger than the true answer. Problems 4 and 8 stay correct.

Subtracting with borrowing
Name ____________Date ________Subtract. Use a pencil.
1.52− 38
2.61− 27
3.75− 48
4.58− 23
5.83− 46
6.45− 18
7.90− 34
8.97− 45
9.63− 25
10.71− 44
11.86− 57
12.42− 19
looplearning.org

What to do this week

  1. Day 1: Use dimes and pennies, or base-ten blocks if you have them. Lay out 52 as 5 dimes and 2 pennies. Ask your child to take away 38, which is 3 dimes and 8 pennies. They only have 2 pennies, so they can't. Pause when they notice they only have 2 pennies, and don't tell them the trade. If they get stuck, ask what a dime is worth in pennies. Once they trade one dime for 10 pennies, they have 12 pennies and 4 dimes, and the taking away works.
  2. Day 2: Same problems, now on paper. Before each ones column, have them say out loud: "Is the top number big enough?" In 52 − 38, is 2 big enough to take 8 from? No, so trade first. Then have them cross out the 5 and write a 4 right away, before they touch the tens.
  3. Day 3: Do the printable again and count how many are still 10 too big. If most of the ten are right now, you're good. If they're still getting the same wrong answer, do Day 1 again.

LOOP does this for every page. Your child does a printed page in pencil. You take a photo. LOOP tells you which mistake showed up on each problem and prints the next page. Your child works on paper the whole time.

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Tyler Judson, LOOP co-founder. Before LOOP I tutored math, one kid at a time. LOOP is my try at giving every kid that kind of attention without a tutor in the room.

The mistake names are the ones LOOP uses, examples checked by running LOOP's mistake-finder.

Know what your child is missing, on paper.

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