An amusing puzzle appears in a recent book by John A. Adam (2013). The answer is very surprising. The book argues in terms of simultaneous equations. A simpler argument, using the diagram below, should make all clear.

**The Watermelon Puzzle.**

A farmer brings a load of watermelons to the market. Before he sets out, he measures the total weight and the percentage water content. He finds that the total weight is **100kg** and the water content is **99%**.

The weather is hot, so his load loses some moisture en route. He checks the water content when he arrives at the market: it has dropped to **98%**.

**QUESTION: What is the total weight of the load on arrival at market ?**

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Most people would guess something around **98** or **99kg**.

This is very wide of the mark.

Think again before you read on.

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Initially there is **99%** water and so **1%** pith. At the market, there is **98%** water, and therefore **2%** pith. The percentage of pith has doubled. *But the actual amount of pith is unchanged*. The only way this can happen is if the total weight is halved!

**ANSWER: T he weight of the load on arrival at market is 50kg.**

The answer is quite surprising. The illustration below should make everything clear:

**Source:**

John A. Adam, 2013: *X and the City: Modeling Aspects of Urban Life*. Princeton Univ. Press. 336 pp. Paper ISBN: 9780691162324. Cloth ISBN: 9780691154640.