# When did the term and taught technique 'cross multiplication' enter into common use?

The title says it all, I suppose. I'm interested to know when/where the term/technique cross multiply came into use. Sources would be nice.

In case it's unfamiliar to anyone, or in case the usage of the term varies, I'm referring to the compound arithmetic operation where an equation of two fractions is multiplied on both sides by its two denominators. It's named because it can be illustrated with a big cross:

$$\frac{a}{b} = \frac{c}{d}$$ $$ad = cb$$

• According to link it was early 1950's Nov 20, 2015 at 2:45
• Ah, the old fashioned dictionary.com Nov 20, 2015 at 2:47
• A quick check of google scholar suggests: <Short, R. L. (1939). Methods in Arithmetic and Algebra. School Science and Mathematics, 39 (3), 239-250.> as a possible source. ("To prove this, just cross multiply numerators and denominators") One issue is that the term cross multiplication had a different meaning before its use in solving proportions... Nov 20, 2015 at 3:03
• Aren't methods for solving proportions found even in the Rhind Papyrus? Or is this question merely asking when the name "cross multiply" was used for it? Nov 20, 2015 at 15:23
• @GeraldEdgar Certainly people have been solving these problems for a very long time. I'm interested in the particular term, and more specifically in its emergence as a pedagogical tool using the mnemonic of the cross. Nov 20, 2015 at 19:06