Allegedly, only .01% of all human beings can solve this Facebook riddle correctly:

1 + 4 = 5

2 + 5 = 12

3 + 6 = 21

8 + 11 = ?

For visual (or video) learners, here’s one explanation regarding the correct answer:

For more literal learners, one approach is to add the first number (let’s refer to it as “a”) to the product (multiplication) of both numbers (we’ll call the second number “b”). With all of this in mind, the equation becomes a + ab as opposed to simply a + b:

1 + 4 becomes 1 + 1(4) = 5

2 + 5 becomes 2 + 2(5) = 12

3 + 6 becomes 3 + 3(6) = 21

8 + 11 becomes 8 + 8(11) = 96

If this still seems somewhat unintelligible (or even crazy!), consider checking the work by utilizing another approach commonly known as “running total/missing lines”:

1 + 4 = 5

5 + 2 + 5 = 12

12 + 3 + 6 = 21

By way of this technique, the new numbers in each line increase by one, relative to the previous line. So, the running total with the inclusion of the missing lines is a solvable equation:

1 + 4 = 5

5 + 2 + 5 = 12

12 + 3 + 6 = 21

21 + 4 + 7 = 32

32 + 5 + 8 = 45

45 + 6 + 9 = 60

60 + 7 + 10 = 77

77 + 8 + 11 = 96

Even the answer of “96” is in harmony with the previous technique, which is usually a strong indication that it is correct—mathematically speaking, of course.

Sources

Facebook post: https://www.facebook.com/randall.joneslatinjuggalo/posts/1048238075247858

Telegraph article: http://www.telegraph.co.uk/education/2016/04/22/this-maths-problem-has-thousands-of-people-baffled-can-you-work/

Reddit puzzles: https://www.reddit.com/r/puzzles/comments/4gbxst/how_to_come_up_with_the_most_correct_answer_on_a/

*This content was inspired by an amazing article that can be found here.