The maths question dividing the internet

Were you paying attention in maths class? Photo / Facebook

Can you answer this seemingly simple algebra question?

The image has been shared and liked by more than 70,000 Facebook users and has attracted a whopping 480,000 comments.

The maths question that has been causing debate online. Photo / Facebook

"Concentrate because this is tricky - the correct answer is?" the post asks.

Answers have ranged from 22, 23, 44, 48 and 21.

Most seem to agree the answer is 13 - here's why:

x = horse
y = horseshoe
z = boot

x + x + x = 30
3x = 30
x = 10

x + 2y + 2y = 18
10 + 4y = 18
4y = 8
y = 2

2y - 2z = 2
4 - 2z = 2
-2z = -2
z = 1

x + y + z
10 + 2 + 1
13

Others argue that the answer must be 21:

It's 21!!
1 horse = 10 2 horse shoes = 4 (so 1 = 2) 2 boots = 2 (so 1 = 1)
1 + 10 x 2 ( apply BODMAS)
1 + (10 x 2) = 21

It's not the first time a maths question has caused confusion online. Earlier this year a question in a test designed for six-year-olds stumped adults who attempted it, and the internet had a meltdown over the seemingly simple intelligence test.