Originally Posted by ColinsMum
Originally Posted by Val
Originally Posted by Siegler et al Early Predictors of High School Mathematics Achievement
the invert-and-multiply algorithm (i.e., a/b ÷ c/d = ad × bc)
I do hope it was Val, not the authors, who wrote exactly this...

Ouch. Good catch.

I cut and pasted from the paper. I double-checked the final version and a preliminary version written by the authors that I just found.

The preliminary version doesn't have the faulty equation (it has no equation). It's possible that this was a mistake made by someone at the journal. I don't know; I wrote to the corresponding author to alert him to the error, and will report back if he replies to me.