Are you smarter than my third grader?

Mark sent me this brainteaser yesterday.  I never did figure it out on my own, but Joe only took about 10 minutes to get the right answer.

I’m sure it was just because I was cold.

Write this equation down on a piece of paper:

5 + 5 + 5 = 550

Now add a single, straight line segment to make it true.

No fair adding a slash to the equal sign to make it not-equal.

No fair putting the answer in the comments — I’ll give you all 24 hours to see if you can figure it out.

Also:  do any of you out there have a source for more brainteasers like this?  We’d love to challenge the boys with more of them, and if anyone has links, I’d love to know about them.


p.s.  Would you believe that it is snowing AGAIN??????????  No school, AGAIN????  Don’t get me wrong:  if the weather’s bad, we don’t need to be out and about, but honestly:  Mother Nature, please, please cut us some slack.


  1. Jan says:

    I have no clue…. I am so not the math person… but just a thought… you might ask over on MQR in the homeschool forum….

  2. Gayle says:

    Well CRAP, I answered on the wrong post! lol guess that makes me smart as …. an old lady with CRS.

    So, here it is again…..

    I am not sure what you mean by adding another straight line segment, but this would make it true:

    5 + 5 + 5 = 550 – 535

    Do I win?


  3. Suzanne says:

    Hey Gayle — When you write it down on a piece of paper, the only additional mark you can make on the paper is the single straight line. No additional numbers, the line can’t be a curve…

  4. carlafibers says:

    Carla got it, but I’m editing her response so that the rest of you still have a chance to figure it out yourself. 🙂

  5. Lynn Douglass says:

    I am soooooooo not a math person, so I’m totally lost! It figures that Carla would get it! ;-p

    Come on out to visit me, Suzanne! We had the patio door open until just about 10:00 this evening. We worked in the yard today, and it’s like spring!

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