Punchline Algebra is carefully sequenced book to help student understand problems which otherwise take a lot of time and effort to understand. An example is that "What can we say about a monster with five legs", and the answer could be "We can say about a monster with five legs that the monster have a pant or trouser that fits him like a glove."
The punchline in this is that pants fit the monster like a glove, and this highlight the figure "five" for a student in an easy fun way.