When this problem was initially posted on Facebook, it included the claim that only one in 1,000 people could solve it.

The problem:

1 + 4 = 5

2 + 5 = 12

3 + 6 = 21

8 + 11 =  ?

What do you think the answer is?

The problem went viral and generated over 3 million comments with people arguing about the correct answer. What do you think the correct answer is?

Get an explanation of the solution.