This has been floating around on Facebook:

Thousands of comments, all with different answers. :-)

I get 7, using the BODMAS rule. But I note some people refer to the PEMDAS rule. Never heard of it (I assume the last four letters stand for multiply, divide, add, subtract, but what does P and E stand for?), and using it some people get 5, while others get 6 or 7. Does the order in which one multiplies and divides really not matter? It seems not to matter in this particular problem, but I recall having seen cases where it matters a great deal, and you get two completely different answers depending on whether you first divide and then multiply, or first multiply and then divide.

Is the BODMAS rule simply a convention, or are there other reasons why it must be followed?