Math, Time & Money

Multiplication tricks for 9s, 11s and 12s (and when tricks backfire)

Girl on the back-deck steps showing her younger brother the nines finger trick on a fall afternoon

A 3rd grader once showed me the 9s finger trick with the face of someone who had found a trapdoor under math. Fold a finger, read the answer, done. Half of me was delighted, because it works. The other half was already thinking about the worksheet in three months that asks the same fact backward, when the trapdoor turns into a hole in the floor.

The 9s finger trick, and the pattern under it

Kids love this one because it needs no pencil, which puts it ahead of most things in the backpack.

Hold both hands up, palms out, fingers numbered 1 to 10 from the left. For 9 × 4, fold down the fourth finger. Three fingers stand to the left of the fold and six to the right. Thirty-six. Quick, tidy, genuinely satisfying.

The trick works because there's a pattern doing the actual labor. Across the 9s facts, the two digits of the answer always add to 9: 18, 27, 36, 54. And the tens digit is always one less than the number you multiplied by. So for 9 × 7 the tens digit is 6, which forces the ones digit to be 3, and there's your 63.

Another way to see it, and the one I'd rather a kid carry around: 9 × 7 is 70 minus 7. Seven groups of ten would be 70, but each group is one short of ten, so give back seven. That "one less than ten" idea is what turns a party trick into something they can actually use later.

The 11s pattern

The 11s feel like mercy after the 7s and 8s, which have caused many reasonable children to stare at the ceiling as though the answer might be printed in the drywall.

For single digits, the digit just repeats. 11 × 4 is 44. 11 × 8 is 88. Most kids grab this in an afternoon.

Fourth and fifth graders can take the two-digit version. For 11 × 23, split the 2 and the 3 and drop their sum in the middle: 2 plus 3 is 5, so 253. It behaves as long as the middle sum stays under 10. 11 × 34 gives 374. 11 × 52 gives 572. Then you hit 11 × 48, where 4 plus 8 is 12, the middle digit won't fit, and you have to carry to get 528. The cuteness evaporates.

So I don't hand every kid the fancy version. What I want them holding is the reason: 11 × n is just 10 × n plus one more n. Ten 23s is 230, one more 23 is 253. That's the entire machine, and it survives contact with 48.

Close-up of a child's hands held up palms out with one finger folded down above an open notebook

The 12s, where I stop calling it a trick

For 12 × 7, break the 12 into 10 and 2. Ten sevens is 70, two sevens is 14, and 70 plus 14 is 84.

That isn't a shortcut taped onto math. That is the math, and the same move keeps working after the tricks run out. 13 × 6 becomes 60 plus 18. 15 × 8 becomes 80 plus 40. 18 × 4 becomes 40 plus 32.

This is why I push the 12s with upper-elementary kids. They force flexibility. A child who can split 12 into 10 and 2 will eventually split 99 into 100 minus 1, or handle $12 as ten dollars and two while you're standing in an aisle trying to remember whether you already have eggs. That flexible habit is the real point of learning the facts at all, and it's the thing a chant never delivers.

Some classes use the word "distributive" early, which is fine. I wouldn't start there at the kitchen table. Start with "break 12 into 10 and 2," and let the vocabulary arrive once the kid has seen it work.

Where tricks snap: division

Here's the part that never makes it onto the cheerful worksheet.

A kid can own the finger trick completely and still stall out on 54 ÷ 9. They know how to fold down a finger and produce 54; division asks how many 9s live inside 54, and the finger trick has no reverse gear. If the fact lives only in the hands, it often doesn't transfer. What they're thinking isn't "nine groups of six makes 54, so 54 shared into 9s gives 6." It's "I had a way to get 54, and this doesn't look like that way." Which is the same wall that shows up when division first arrives and everything suddenly runs backward.

Place value exposes it too. Ask for 9 × 60. A kid with the understanding says nine sixes is 54, and these are tens, so 540. A kid with only the trick looks at their hands, looks at the zero, and concludes that math has become rude. Fair.

None of which means the trick is bad. Tricks sitting on top of understanding are useful and fast. Tricks standing in place of understanding are flimsy, and they tend to give out in the same week the format of the homework changes. Then a kid who honestly did know this yesterday says "I know this" while the page says otherwise, and everyone at the table gets testy, including the dog. That's a homework problem more than a math problem, and it's worth naming out loud.

How to tell which one your kid has

You don't need a quiz. Please don't build a quiz. Kids already get plenty of pages of naked number problems marching in rows like tiny tax forms.

Ask one calm question: why does that work?

If the answer is "I don't know, it just does," that's information, not a crisis. A few more probes, spread over a week, not delivered in one sitting:

  • "Show me another way to get 9 × 7."
  • "If 9 × 7 is 63, what's 9 × 70?"
  • "How do you know 11 × 23 is 253?"
  • "Can you build 12 × 7 out of 10 × 7?"

You're listening for connections, not vocabulary. Good answers sound plain and a little clumsy. Nine sevens is seventy minus seven. Twelve sevens is ten sevens plus two more. Eleven 23s is ten of them and one extra. That's understanding, and it doesn't have to be elegant.

When it isn't there yet, keep the trick and put meaning next to it for a week. For 9s, draw arrays: six rows of nine dots, then six rows of ten with one crossed off each row, so 60 minus 6. For 11s, write 23 in a stack ten times if that's what it takes to make 230 visible, then add one more. Clunky is allowed. For 12s, use crackers: seven packs of twelve, ten from each pack makes 70, two more from each pack makes 14, and somebody will eat four during the demonstration.

Five minutes a day covers it. One array, one skip-count, one "why does that work." If the facts themselves are still shaky underneath all this, the order you practice them in matters more than the number of repetitions. Keep the finger trick if your kid loves it. Just make sure something is holding it up, because hands are handy and they should not be the entire calculator.

Written by Samantha

Samantha is the numbers half of the two sisters behind Mokifun. She tutored upper-elementary math for years, has two kids in school herself, and writes the pieces about math facts, telling time and money, plus a good share of the everyday school-life ones. She keeps an analog clock in the kitchen on purpose. More about Samantha and Mokifun →

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