Anomalous Cancellation
Number Theory
Level
5
\[\large\dfrac{1\not{5}}{\not{5}7}\ne\dfrac{1}{7}\]
When teaching children how to reduce fractions, many of them will make mistakes like the one shown above. However, there are a few situations in which making this error does yield the correct answer, that is, \(\frac{\overline{AB}}{\overline{BC}} = \frac{A}{C}\). For how many fractions would this method of simplification work?
Note: \(\overline{AB}\) simply denotes the decimal expansion of a two-digit number with \(A\) and \(B\) as the digits.
by
Garrett Clarke