A compound fraction is simplified by multiplying the numerator by the reciprocal of the denominator fraction. This process is repeated as often as necessary at every level of the fraction.
Examples:
(a/b)/(c/d) = (ad)/(bc)
a/(b/c) = (ac)/b
(a/b)/c = a/(bc)
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When the fraction has numerators or denominators that are fractions, you need to be very clear about what is being divided by what. If it isn't clear by the typesetting (length or boldness of fraction bars), then parentheses are required around numerators and around denominators.