Countin' Birdies With Poor Eyesight
A man having his eyesight somewhat altered, began to tell and reckon a certayne number of birdies to be in all 18. His companion that had a clearer sight, beholding wel the birdies, answered him, that ther were not 18, but saide he, if ther were twice so many more as ther are, ther should be as many more about 18, as ther be now less than 18. The question is to know how many birdies ther were in all.
Source: H. Baker, Well Spring of Sciences, which teacheth the perfect worke and practise of Arithmeticke,
both in whole Numbers and Fractions, 1568