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Re:I gave my students iPads – then wished I could take them ... by Retra on Monday December 07, 2015 @09:39AM (#10689670)
The number of people who can do it quickly in their head, maybe. I don't know a single adult who would look at that problem and say they don't know how to solve it.

Math is a perishable skill. You get slow at it if you don't use it.

Re:I gave my students iPads – then wished I could take them ... by matwood on Monday December 07, 2015 @09:56AM (#10689824)
It is just a matter of remembering the tricks. (9x10) + (9x4)