A Smart Housewife.
A smart housewife was told that there was a kind of stove which would only consume half of the coal she was burning. She was very excited, and said: "That'll be terrific! Since one stove can save half of the coal, if I buy two, no coal will be needed!"
English translation
精明的家庭主妇
一位精明的家庭主妇听人说有一种炉子用起来可以比她现在用的炉子省一半的煤。她听了大为兴奋，说：“那太好了！一个炉子可以省一半的煤，那么如果我买两个炉子的话，不就可以把煤全都省下来了吗？”