Is there a phrase that is the opposite of "putting two and two together"? [closed]

I've been looking for a phrase that would describe the opposite of putting two and two together.

For example:

"I thought Cindy's murder had everything to do with Mark's disappearance, but as it turns out, instead of putting two and two together and getting four, I put two and two together to get five, not realizing it was actually her estranged son that had done the deed!"

Or as someone else put it, I'm looking for a better way to say "I came to the wrong conclusion"

Solution 1:

Debunk, as in I debunked the idea of a correlation between A and B.

Defined by Google as:

expose the falseness or hollowness of (a myth, idea, or belief)

Solution 2:

How about: "I divided by zero and got nothin'"

Solution 3:

You could say It turned out A and B were orthogonal.

(Of variates) statistically independent.