Recovering a whole from a fractional part of it
Worked examples: 3 as 3/4, 17 as 4/5 and 19 as 13/17 of a number
A continuation of the fraction exercises, written upside down. Leonardo gives the general recipe for finding the whole number of which a given quantity is a stated fraction: divide the quantity by the numerator and multiply by the denominator. He works three cases in turn: 3 as 3/4 of a number, 17 as 4/5, and 19 as 13/17.
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General method for fractional parts
To find the number of which 3 is 3/4, divide 3 by 3 to get one, then multiply that by 4 to get 4. He calls this a simple example of the operations to come, and applies it to 17 as 4/5 (divide by 4, multiply by 5) and to 19 as 13/17 (divide by 13, multiply by 17).