I carried 1000 Kg of watermelon in summer by train . In the beginning the water content was 99%. By the end of journey , the water content to 98%. The reduction in the weight of water melon was__________. ( ans 500 Kg). How is it possible. It is a KVPY Q

Rather than thinking about the part of the watermelon that is water, think in terms of the part that is not water. This part does not change during the journey.

At the start 1% of the 1000 kg watermelon is not water, that is 10 kg of the watermelon is not water. After the journey this 10 kg of material is 2% of the watermelon since the part that is water is 98%. The problem can thus be reworded to ask, what weight is a watermelon if 2% if it weighs 10 kg?

Suppose the watermelon weighs W pounds then 2% of W is 10, or W(2/100) = 10 so W is 500 kg.