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Homeschool math, Grade 5, multiplying by a one-digit number

Why does my child add the carried number too early in multiplication?

For example: 256 × 3 = 988

The right answer is 768. Your child wrote 988 because they added the carry to the digit first and then multiplied, instead of multiplying first and then adding the carry. Lots of kids do this. It's fixable, and you can start tonight. In LOOP we call it "Added the carry before multiplying."

Your child isn't being careless. They know there is a carry and they know it gets added. They just put it in at the wrong moment. The order matters, and 256 × 3 is a good one to see it in.

What they wrote256× 3988
The right answer256× 3768
Here is what happened. The ones went fine: 6 × 3 = 18, write 8, carry 1. Then they added the carry to the 5 first and did (5 + 1) × 3 = 18. Write 8, carry 1 again. In the hundreds it was (2 + 1) × 3 = 9. So the answer came out 988.

Here is the right way. Multiply first, then add the carry. 6 × 3 = 18, write 8, carry 1. Next 5 × 3 = 15, and 15 + 1 = 16. Write 6, carry 1. Last 2 × 3 = 6, and 6 + 1 = 7. The answer is 768.

Is it this, or something else?

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

988Added the carry before multiplying. This is the page you're on.
658Dropped the carries. They wrote the ones digit of each product (8, 5, 6) and never added the carried numbers.
758Their method is fine; one fact slipped. Check which fact: 5 × 3 = 15 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 (321 × 3 and 412 × 2) have no carries at all, so they are your check. If those two come back right and the other ten are all wrong in the same way, this is probably the mistake. Check the key below for the exact wrong answers.

It prints on its own page.

Answer key

1. 768, 2. 696, 3. 1,900, 4. 815, 5. 861, 6. 2,144, 7. 1,854, 8. 1,490, 9. 774, 10. 1,970, 11. 963, 12. 824.

A child making this mistake will write 988, 806, 2,860, 2,055, 1,501, 2,804, 1,894, 1,600, 3,024, 4,050 for problems 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. Problems 11 and 12 stay correct.

Multiplying with carrying
Name ____________Date ________Multiply. Use a pencil.
1.256× 3
2.348× 2
3.475× 4
4.163× 5
5.287× 3
6.536× 4
7.618× 3
8.745× 2
9.129× 6
10.394× 5
11.321× 3
12.412× 2
looplearning.org

What to do this week

  1. Day 1: Do 256 × 3 with base-ten blocks, or with sticky notes: 2 hundreds, 5 tens, 6 ones, three times over. Ask your child to count the ones first. 18 ones is one ten and 8 ones. Have them move that ten over to the tens pile. Now count the tens: 15 tens from the three groups, plus the 1 that moved over is 16. Don't tell them the order. Let them see that the carry joins after the groups are counted.
  2. Day 2: Same problems, now on paper. For each column, have them say out loud: "Multiply first, then add the carry." In the tens of 256 × 3, that is 5 × 3 = 15, then 15 + 1 = 16.
  3. Day 3: Do the printable again and count how many are still wrong. 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 for Grade 5 multiplication. The examples were checked by running LOOP's mistake-finder.

Know what your child is missing, on paper.

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