Divided by half - meaning

If someone says "Fifteen divided by half", I would interpret that literally to mean 15/0.5, or 30. However, I usually see it interpreted as 15/2, or 7.5.

Which interpretation is correct?

Solution 1:

It's simply grammatically incorrect, so it has no literal meaning. (And before anyone shows up to argue against prescriptivism, the very concept of a "literal meaning" contrary to what is meant/understood is prescriptivist at a basic level)

You could say "divided by one half", or "divided by 0.5" for one meaning; or "divided in half" for the other.

Solution 2:

You're right. Fifteen divided by half is 30, and that's that. Any other interpretation is incorrect. However, fifteen by half could be interpreted as fifteen [multiplied] by half, which would then give ¹⁵/₂ or 7.5.

Solution 3:

As others have said, it's probably a grammatically incorrect attempt to say something was halved. It seems to be a somewhat common mistake if my peers in math classes are any indication. It seems to me to be a mix-up of "divided in half" and "reduced by half".