3 ms·

I was never even taught this "trick." The language used is shitty. The way I was taught, dividing a fraction by a fraction is equivalent to multiplying the fir

• xtreme 11y ago
  You are definitely judging the book by its cover. If you follow the link, the full book has a lot more "tricks" and "solutions". The cross-multiply one is just an example. Of course many of them are culture/location dependent, but I'm sure you will find ones that you are familiar with.
• eterm 11y ago
  I guess it is saying that people are going straight to the "trick" (multiply the reciprocal) instead of understanding that they are applying the fact that: a / (b/c) = a * (c / b) (a in Q, b,c in N and b <> 0) And that they therefore have a less rich understanding of when the rule is applicable and when it isn't appropriate. (Such as a situation where b is actually zero, perhaps if it's "hidden" in another form like x-y.