A month ago I posted another picture algebra maths puzzles. This time it was the Clocks, Calculators and Lightbulbs algebra maths puzzle which looked simple but had more to it than you would initially think.
[Edit] This puzzle was originally created by Leander from 123 Puzzle Me.
If you have not had a go at solving this puzzle and registering your answer on the poll; Stop reading the solution, click on the link above and go do it now. 🙂
The puzzle image is shown below:
And here is the “initial” solution:
- There are three clocks which total 21, so each clock is 7.
- There are three calculators which total 30, so each calculator is 10.
- There are two lightbulbs added and one subtracted, so each lightbulbs is 15.
- The final sum is 7 + 10 x 3(15) which equals 7 + 10 x 45.
- Doing Multiplication first gives 7 + 450.
- So the final answer is 457 …… WRONG.
Look closer at the image and you will notice the following:
- The clocks hour hour is pointing to different hours.
- The calculator digits are not always the same.
- The lightbulbs have different number of “glow” lines.
So let’s start again, with the correct solution:
- The clock hour hands point to 9 + 9 + 3 = 21, so we must use the hour hands.
- The digits on the three calculators (1234) add up to 30, so we must use the sum of digits.
- The three bulbs have 5 “glow” lines each, so we must use these lines with value 3.
- In the final sum, the clock is 9, the calculator adds up to 9 and the bulbs have 4 lines.
- The final sum is 9 + 9 x 3(4×3) which equals 9 + 9 x 3(12) = 9 + 9 x 36.
- Doing the Multiplication first gives 9 + 324.
- So the final CORRECT answer is 333.
Were you really observant? Did you get it right? At the time of posting the solution, 48% of respondents on the poll were correct, which is pretty good.
[Edit] The videos below explain some additional details not noticed before and so changes the value of the correct answer:
Clock, Calculator, Bulb Puzzle Explainer, by the creator. (direct link)
Viral Clock Calculator Light Bulb Puzzle – The Correct Answer Explained (direct link)
Keep safe, well and sane.
David
12-Nov-2024: Added link to video from MindYourDecisions YouTube channel.
07-Oct-2025: Updated image with original from 123 Puzzle Me. Also added explainer video from the creator.
This article was originally posted on http://www.winthropdc.com/blog.
The glow lines on the lightbulb got me! Thanks – this was fun 🙂
I still don’t ge the bulb part… Though i understand the lines but why are we using the value 3?? From where does 3 come??
Hi HY
The sum that defines the lightbulb glow lines has a minus sign which cancel out two of the bulbs. So each glow line is 3. If it had been a plus sign then each glow line would be one. Is that what you missed?
David
The question is ill-defined. There are many different consistent answers and unless it’s a mind reading exercise, none of them can be called wrong.
Not ill-defined, you just need to be observant and see the small details.
The YouTube channel MindYourDecisions brought up an interesting detail that changes the answer considerably: The bulbs have different numbers of rings on their bases as well as different numbers of rays. The first set of bulbs with the 5 rays have 3 rings, which is where the 3×5 comes into play. But two of the final bulbs have 4 rings while the remaining bulb has 3, so it would be the only bulb with the multiplier of 3. So the bulb section of the last line becomes 4 x 3 + 4 x 4 + 4 x 4. Do the multiplications and you get 12 + 16 + 16, which equals 44.
So that makes the final line 9 + 9 x 44. Do the multiplication to get 9 + 396, which gives us the more likely correct answer of 405.
Interesting. Not sure the screw rings on the final “equation” are clear enough to be counted. At least on the image I used. I have added a link to the video with the clearer image.
I’m going to take the argument one step further, I believe the answer is actually 27,657.
Everywhere else in the presentation of this problem the addition or subtraction sign is used between representative symbols;
Line 1 we have 9 + 9 +3 = 21 (Based on where the Hour hand is pointing);
Line 2 we have 10 + 10 + 10 = 30 (Based on the sum of the numerals on the calculator);
Line 3 we have 15 + 15 – 15 = 15 (Based on each globe having 5 rays and 3 rings);
On the final line we have a Clock face representing a 9, a calculator representing 9 also, and then 3 globes all with 4 rays, but only 2 with 4 rings and 1 with 3 rings, giving what appears to be 3 globes representing 16, 16 and 12.
So the final line would appear to be 9 + 9 x 3 globes with the values of 16,16,12 but unlike the other lines there is no + or minus operand between the globes.
I would interpret this as 9 + 9 x (16x16x12) and therefore 9 + 9 x 3072 which would become 9 + (9 x 3072) which would equal 9 + 27,648 = 27,657.
Also to throw a further spanner in the works, I heard mention in the YouTube video above that the rings on the globes were threads, if that was in fact the case then each globe, being Edison Screw globes, only has one thread…
Valid points and I have added the video with clearer image, but I think you have too much time on your hands to think about this problem. 😊
The designer of this puzzle is Leander from 123 Puzzle Me. Maybe you should give him some credit instead of MindYourDecisions, who just posted a poor copy of the original design.
As for the solution — 333 is the only logical answer.
Thanks for letting me know. I have updated the image with the original and given credit in both articles. It is not always possible to identify the creator, but I always try to give credit.