The puzzle, from a Hong Kong primary school admission test for six-year-olds, is supposed to be solved in under 20 seconds.

It has now gone viral, perhaps because of its absurd simplicity when actually worked out. (Spoiler: the answer is below, but try and figure it out on your own first!)

Based on the visible numbers in the image above students are asked to work out the number hidden by the parked car. The numbers - 16, 06, 68, 88, X, and 98 - don't exactly lead to any quick pattern recognition.

Don't be too annoyed if you can't figure it out straight away.

Adults tends to overthink the numbers presented and attempt to work out some kind of complex algebraic pattern.

Children are more used to solving problems from a range of different angles, rather than any tried to true solutions.

British puzzle designer David Bodycombe told The Guardian he came up with the puzzle back in the 90s while parked in a car park in Portugal.

He had no idea that any Hong Kong schools were using his puzzle, and had not received any compensation.

Have you figured it out yet?

Why not try flipping the image upside down.

The answer is 87 - and the pattern is simple counting.

Stuff.co.nz