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If you give away seven cents, what is the probability of getting a $1.75 in return?

I told my after-school tutoring kids we were going to work on probability.  I handed each of them a penny.  As I pressed the penny into each student’s palm, I said, “Here.  I want this quarter back when we are finished.”  Each child looked at his or her penny and said, “Okay.”

A Title One (NCLB) inspector was in the room watching.   She chuckled.  “You just taught me something,” she said.  “If this works, I’m changing jobs.”

I told the students to look a their pennies closely, then record in their notebooks the chance of flipping that penny into the air, and having it land heads up.  All four of the fifth graders and one of the fourth graders wrote 50%.  The other two fourth graders weren’t certain.  With a little prompting they came to realize their coins only had two sides and, if tossed, would have to land on one or the other.  They each wrote down “half.”

They all flipped their coins 100 times and tallied heads or tails, proving that indeed, their 50% predictions were very accurate.   The next thing I did was hand each child a die and ask them make the same sort of prediction for the number five.  They all figured out very quickly the odds would be one in six, of obtaining a five.  I asked them to record in their journals which of the two games they thought would have the best odds in winning, and explain why.

After they settled to write, I said, “I need my quarters now.”  They all tried to hand me the pennies.   “No,”  I shook my head and pulled my hand away.  “You said you’d give me quarters.”

Andi’s eyes grew wide.  “We did!” She exclaimed.

Bill handed me his penny again.  “Here’s your quarter, Ms. A.”  he said.

I said, “Bill, this is a penny.  I want a quarter.”

He answered, “Your odds of getting one are zero out of seven.”

The inspector gave me an A+.

Quilly is the pseudonym of Charlene L. Amsden, who lives on The Big Island in Hawaii. When she is not hanging out with Amoeba, she is likely teaching or sewing. Or she could be cooking, taking photographs, or even writing. But if she's not doing any of that, she's probably on Facebook or tinkering with her blog.


  1. Brig — the classroom door is open. Stop in.

    Bill — it has to do with required curriculum, but you’d better believe I took the time to explain house odds. Now if they’ll just go home and teach it to their parents!

  2. Good move – explaining the house odds. Everytime I pay a jackpot I remind the guest that if they don’t head straight for the door, odds are good that we’ll get our money back.

    I like the fact that you are not a straight-from-the-textbook kind of teacher. I’m sure your students appreciate it, too.

  3. Rob — is that bit of info casino policy, or your own brand of concern? How do your bosses feel about you telling people to take the money and run?

  4. Wow, that must have been interesting. Kids need more teachers like you! Brava! Around here techers have to spend so much time teaching for the standardized tests they forget to teach. Then they get mad if they don;t get a bonus or don’t get a big enough one!

  5. LOL!! Poor Andi. Teaching kids panic as well as odds …

    Rob, if there’s anyone like you where you work, then the casino operators are behaving better than Your Elected Officials and their [Name Your State] Lotteries …

  6. Wow, Quilly, teaching them how to gamble, huh? Well, you’re in the right city! I’d have given you an A+, too – learning should be fun.

  7. Well! They’re better at odds than they are at negative numbers!!! Perhaps you should use “gambling” to teach THAT too!

  8. Jill — if they’d let us do more teaching, the tests would take care of themselves. For years I have been saying, quit changing the procedures and curriculum every year. Give somehing a chance to work. he school I am a now has used the same programs for 6 years. I don’t think it’s an accident that this year I have one of my highest performing classes ever.

    OC — for some reason my students quickly learn to suspect my motives, and question everything. I don’t know why they fell for this, but it was fun.

    Jackie – hopefully teaching them not to gamble! They figured out quickly that the odds weren’t in their favor.

    Donna — I hope i also shows in their willingness to make those come backs. I used to think such hings as a kid, but my continuing life is proof I never said them.

    Melli — I just might at that!

    Polona — neither tteaching or gambling are good get rich quick schemes.

    Dr. John — great kid stories are easy to come by when one has great kids.

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