Have you ever stopped to consider how much watermelons weigh, especially when their water content changes? This seemingly simple question can lead to surprising insights into weight, percentages, and even problem-solving skills. Let’s dive into the juicy details.
Imagine a scenario: A neuroscience professor at Harvard poses a brain-tickling question during an interview. It’s not about complex research, but a seemingly simple math problem designed to test critical thinking.
The Watermelon Riddle: A Weighty Problem
Here’s the question that stumped a group of highly educated individuals at a summer BBQ:
A 100kg watermelon is 99% water. After sitting in the sun, it’s 98% water. How much does the watermelon weigh now?
The most common initial answer? “99kg!” The reasoning seems straightforward: the watermelon lost 1% of its water (99%-98%=1%), which equates to 1kg (1% of 100kg). Therefore, the new weight must be 99kg.
However, this is incorrect. The correct answer is 50kg.
Why the Initial Answer Is Wrong
The initial, intuitive answer overlooks a crucial detail: the percentage change affects the entire weight composition, not just the water content directly. The key is to focus on the non-water component.
The Correct Solution: Focusing on the Constant
Here’s how to arrive at the correct answer:
- Initial State: The 100kg watermelon is 99% water, meaning it contains 99kg of water and 1kg of solid mass (non-water).
- The Constant: The solid mass does not evaporate. So, even after sitting in the sun, the watermelon still contains 1kg of solid mass.
- New Percentage: After being in the sun, the watermelon is 98% water, meaning the 1kg of solid mass now represents 2% of the total weight.
- Calculating the New Weight: If 1kg is 2% of the total weight (x), then we can set up the equation: 1 = 0.02 * x. Solving for x, we get x = 50kg.
Therefore, the watermelon now weighs 50kg.
The Takeaway: Beyond Watermelon Math
This watermelon problem illustrates a broader principle: Don’t always trust your initial, gut reaction, especially when dealing with calculations. Even intelligent and educated people can make mistakes by rushing to an answer that seems obvious.
The real lesson here isn’t about watermelons, but about the importance of critical thinking and double-checking your reasoning. Taking a few extra moments to confirm your answer can make all the difference, whether you’re solving a math problem or making a critical decision.
Confirming Your Intuition
So, should you always ignore your gut feeling? Not necessarily. What you should do is take a few extra moments to confirm that your intuition is correct. This is especially important for problems that involve calculations.
