A graphic shows a series of odd math equations and asks readers to fill in the final answer. How would you solve this equation and what answer do you think is best? Our readers have debated the problem for over 2 years.
Math Riddle
First, let’s take a look at the riddle itself. The image below has circulated on social media for over two years. It contains the following math problem, often with a caption that reads:
We can’t figure this out… Can you? 92% of people fail it. Good luck!
1+5 = 12
2+10 = 24
3+15 = 36
5+25 = ?
After considerable debate here, we’ve come to the conclusion that there are four popular ways to solve this, resulting in two different answers.
Answer 1 – Pattern Theory
If we view the problem as a pattern, and not 4 separate math problems, then the answer to “5+25=” should be 60. If this is a pattern, then one row of the pattern was omitted. Consider looking at the problem this way:
| 1 | 5 | 12 |
| 2 | 10 | 24 |
| 3 | 15 | 36 |
| 4 | 20 | 48 |
| 5 | 25 | 60 |
If we view the equation in the manner above, then “4+20 = 48” was omitted from the original problem for reasons unknown. As you can see, however, the pattern theory holds that each column is its own pattern. The first column increases by 1, the second column increases by 5, and the third column increases by 12.
Answer 2 – Days and Weeks as Units
Another solution – which also yields an answer of 60 – holds that the first two columns equal units of weeks and days respectively, and the third column represents days. Thus:
1 week + 5 days = 12 days
2 weeks + 10 days = 24 days
3 weeks + 15 days = 36 days
5 weeks + 25 days = 60 days
Answer 3 – Trick Question
If we look at the problem literally, then the answer to “5+25″should be 30. The logic here is that 3 incorrect answers in a row should not affect the answer to the problem posed to readers. Thus, 5+25 should be 30.
Answer 4 – Dr Dave’s Fibonacci series
As commenter DrDave points out below, this problem is a “Fibonacci series.” Even though he, too, comes up with 60 as an answer, his method is different than what we presented above. Although his explanation is in much more detail, perhaps the easiest way to look at it is to ignore the + and =, and just add the numbers in two columns to determine the next value. Thus:
1 5 12
+2 +10 +24
—————–
3 15 36
Then:
2 10 24
+3 +15 + 36
——————
5 25 60
Readers
The overwhelming opinion of commenters on our Facebook page is that the answer should be 60, although the ways of achieving answer this vary greatly.
Your Turn
What solution do you feel is the best to solve this problem? Do you have another theory that we didn’t pose here? Let us hear from you in the comments below.
Updated May 30, 2015
First published April 2013
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