# keep-flip-change

Let $a,b,c,d\in\mathbb{Z}-\{0\}$. A mnemonic device for calculating

 $\frac{a}{b}\div\frac{c}{d}$

is KFC. This stands for ”keep-flip-change”. This means that you keep the first fraction as it is, flip the second fraction, and change the problem to a multiplication problem. Thus, the expression above becomes

 $\frac{a}{b}\cdot\frac{d}{c}.$

This yields that

 $\frac{a}{b}\div\frac{c}{d}=\frac{a}{b}\cdot\frac{d}{c}=\frac{ad}{bc}.$
Title keep-flip-change Keepflipchange 2013-03-22 15:59:52 2013-03-22 15:59:52 Wkbj79 (1863) Wkbj79 (1863) 4 Wkbj79 (1863) Definition msc 97D40 KFC K.F.C.