Given the fraction 471428/714285, strike out the 71428 on the top and bottom to get 4/5, which does not equal 471428/714285. This recipe almost never works.[more]
However, 4571428/5714285 does equal 4/5, the result of striking out 571428 on the top and bottom. Very rarely, this bad method of simplification actually works. When it does, there is a repeating decimal of another fraction involved.
Bad fractions can quickly get enormous. One example is 73/81, which uses the repeating decimal of 5913/7219 with length 7218.[less]