I am embarassed to ask this question, but when a fraction divides a number, the rule is:
$\dfrac{a}{\dfrac{b}{c}}$ it is supposed to be $\dfrac{a\cdot c}{b}$
$\dfrac{\dfrac{a}{b}}{c}$ it is supposed to be $\dfrac{a}{b\cdot c}$
Notice the bar for diving fraction is different, in the first fraction it is longer for $a$ and $b$, while in the second it is longer for $b$ and $c$
So which rule should I use? I thought division of a number means multiplying the inverse of that number, am I correct?
The longer bar means there are parentheses around the stuff above and below. So $$\dfrac {\dfrac ab}{\dfrac cd}=\dfrac {\left(\frac ab\right)}{\left(\frac cd\right)}=\frac{ad}{bc}$$ where the middle bar is supposed to be longer in the first fraction.