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Brain Teaser: What’s the Mystery Number?

Allie Johnson

Do you hate being kept in the dark? An unsolved mystery can haunt you, rattling around in your brain like a ghost.

We may never get answers to some of history’s biggest mysteries, such as the truth about the Bermuda triangle, the location of Cleopatra’s tomb or the identity of Jack the Ripper.

But we have an enigma you can solve in minutes, and it may even help to keep your brain sharp. Brain teasers like this one may boost your language ability, memory and problem solving skills.

If you’d like to play detective, this mystery number brain teaser will require you to use both logic and math skills. Using only the numbers on the page as clues, you’ll have to decipher the identity of the final missing number.

Math games like this one may help keep your brain strong and flexible through development of new neural connections. Number games also may make you quicker at everyday calculations, from figuring out how many bags of Halloween candy to buy to making sure you get the right amount of change back at the store.

Check out the bottom of the page for the correct answer.


Answer: 17 | The middle number equals the top number times the bottom number plus the left number times the right number.


Did you solve the mystery number puzzle? If so, please comment to clue us in on how you did, how long it took and what’s your favorite unsolved mystery.

What’s Next?

Did you know that brain teasers like this can help keep your brain in shape?  Learn more about strengthening your brain…

49 Responses to "Brain Teaser: What’s the Mystery Number?"
    • Angela Moore-Colley | December 25, 2020 at 7:53 pm

      Fun! Took about a minute to see the number relationship.

    • Peter | October 31, 2020 at 12:22 am

      That was fun. I’d say about 2 minutes or so to get the answer.

    • Raymond Whitehead | October 27, 2020 at 7:58 pm

      It took me ten seconds, but then, i am a math professor. Using the numbers 1 through 9 only once each, and using add, subtract, multiply and divide each once only, come up with the number 100. Santa Fe Ray

    • Donna | October 27, 2020 at 9:41 am

      I tried adding two numbers and then the other two numbers and seen immediately that wasn’t correct. I multiplied two numbers and the other two numbers and that was the answer. Took me right under 2 minutes for solve. Makes ya think:)

    • Jerry N. | October 26, 2020 at 1:37 pm

      Took ~5 minutes; being an avid backgammon player helped.

    • Art | October 25, 2020 at 11:52 pm

      (1 x 3) + (4 x 5) = 23

    • Kevin | October 25, 2020 at 9:07 pm

      Took me a little over 2 minutes but then I was watching the Seattle Seahawks beat up on the Arizona Cardinals while figuring it out.

    • Marty A | October 25, 2020 at 4:28 pm

      More Please! Added the individual numbers mentally, hmmm, then tried multiplication across and then up and down, added the sums, and then smiled. A few seconds total, but enjoyable non the less. Don’t overthink the examples.

    • LARRY D SNORTLAND | October 25, 2020 at 1:48 pm

      I substracted 30 from 43 & 13 from 30=17

    • M D Anderson | October 25, 2020 at 11:56 am

      It took longer to find a paper and pencil than to find the number.

    • Nancy | October 25, 2020 at 10:36 am

      It took me 20 seconds. To Larry and Gary. #1. 3 x 5 = 15. 4 x 7 = 28. 15 + 28 = 43. #2. 6 x 2 = 12. 2 x 9 = 18. 12 + 18 = 30. Therefore 3 x 4 = 12. 5 x 1 = 5. 12 + 5 = 17. Hope this helps clarify the answer. I love puzzles. Give us more!

    • Rob | October 25, 2020 at 7:50 am

      Good brain teaser, send out more

    • Debbie Owens | October 24, 2020 at 8:47 pm

      30 seconds and done!

    • g heinz | October 24, 2020 at 8:12 pm

      15 seconds. Fast with numbers slow on reading

    • Manaloor Abraham | October 24, 2020 at 6:22 pm

      good brain teaser but not time killer either.

    • Patricia Schmit | October 24, 2020 at 4:48 pm

      Less than two minute Love puzzles like these!

    • JEFFREY D ROSS | October 24, 2020 at 1:56 pm

      Cool math puzzle took 45sec

    • Pete Baird | October 24, 2020 at 1:47 pm

      I made it overly difficult with an answer 23

      Difference between Top & right numbers = first number
      Difference between bottom and left numbers X 3 = second number.

    • Laurie Marinelli | October 24, 2020 at 11:46 am

      Took me 2minutes and 15 seconds to come up with the answer of 17. I really love math so I found this very easy. I my really did make me think.

      I compared the first example to the second example. I came up with a theory on how they actually work. I looked at the puzzle and was able to solve it in a reasonable amount of time.

      I would love to see more puzzles that require math skills!

    • DON COX | October 24, 2020 at 11:19 am

      ABOUT 2 MIN. TOP TIMES BOTTOM + SIDE TIMES SIDE ADDED = MIDDLE

    • Mary S Lake | October 24, 2020 at 11:05 am

      Love numbers…this one was easy.

    • Thresa Clements | October 24, 2020 at 11:00 am

      I first did combinations of adding and subtracting before trying multiplying. Took me about 5 minutes.

    • Verril Gamet | October 24, 2020 at 11:00 am

      Since 43 is a prime number, I could rule out multiplication to get the final equation. So all total, maybe 2 minutes.

    • James Schings | October 24, 2020 at 10:09 am

      Yep 19. Took about a couple minutes. Only because I did the math about 10 times because it seemed too obvious and though there was something I was missing.

      Not sure what Larry Bowser and Gary Loper are saying ?

    • Judy Adams | October 24, 2020 at 10:07 am

      about 15 seconds to solve

    • Irene Bryant | October 24, 2020 at 9:48 am

      I love it . It Was great. Help me so much. I need More like this. It got me going. Thanks.

    • Richard C Evans | October 24, 2020 at 9:40 am

      My first thought was to operate on the numbers in some way. I immediately realized adding wouldn’t do it. So, I tried multiplying in pairs and adding and that worked. The trick to solving puzzles is the kind of strategies one has available to solving puzzles. Let me share a puzzle with you. Using all the numbers 1 – 9 form 2 3-digit numbers that add up to the last 3 numbers. There are 168 solutions to this problem. The real test is to see how many you can find.

    • Beverly Frizzell | October 24, 2020 at 9:37 am

      I multiplied the 2 horizontal number and the 2 vertical numbers and added them together. Solved in less than 30 seconds.

    • Jake | October 24, 2020 at 9:23 am

      the number is 17….took me 1 1/2 minutes to figure out

    • Frances Mabry | October 24, 2020 at 9:19 am

      I solved in maybe two minutes. Please include more of these, please!

    • JAY H Kim | October 23, 2020 at 12:53 pm

      Great brain puzzle.

    • David T R | October 23, 2020 at 11:50 am

      30 seconds… while watching TV

    • Barbara Dauerty | October 23, 2020 at 11:38 am

      The solution took about 2 minutes. I tried adding all surroundin numbers first, then hit on multiplying opposite numbers and adding the results.
      Nice!

    • Lorna | October 23, 2020 at 11:33 am

      I love puzzles and math. Took about 1 minute.

    • JOAN BLACKBURN | October 23, 2020 at 11:15 am

      Took 2 mins. Enjoyed the challenge

    • Tom | October 23, 2020 at 10:40 am

      I subtracted 30 from 43 and 13 from 30 about 2 minutes

    • Sandra | October 23, 2020 at 10:14 am

      17

    • Bev Crites | October 23, 2020 at 10:02 am

      It took just over a minute. Just adding and multiplying until it made sense.

    • Gary Loper | October 23, 2020 at 9:40 am

      Larry Bowser is right. The first 2 do not add up like you say.

    • tazmanthe1st | October 22, 2020 at 8:24 pm

      About 1 1/2 minutes.

    • Deborah | October 22, 2020 at 6:59 pm

      I actually solved the 2nd puzzle 1st. I times the 2 numbers across and the times the 2 numbers up and down. Once I had those numbers, I just added them together to get center number. About 3 minutes. Keep am coming!

    • Larry bowser | October 22, 2020 at 1:26 pm

      the first two do not add up to the middle number so what do the first two have in common with the third.

    • Joy Goff | October 22, 2020 at 12:20 pm

      Solved in about 3 minutes

    • Melany Baggs | October 22, 2020 at 11:46 am

      I multiplied the cross numbers then added them together for answer. I love puzzles. Word search, what’s different, fill ins. Thank you I enjoyed very much. Please provide more. Oh, took less than a minute to solve.

    • Annette Alfaro | October 22, 2020 at 11:41 am

      I love these and my grandsons love to help with the challenge. More puzzles like these please.

    • Adwait | October 22, 2020 at 11:39 am

      It took about 2 minutes.

    • Rosalie Hoffman | April 25, 2020 at 3:04 pm

      Give me more of puzzles like this one!!!!!!!!!

      • Shirley | January 23, 2021 at 8:20 pm

        Missed the timer, but did just fine.

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