If the watermelon that weighs 20 kg has 98% water, we should first figure out what the weight of the other 2% is.
Weight of entire watermelon: 20 kg
Weight of the water: 20kg (0.98) =19.6 kg
Weight of the other part: 20kg (0.02) = 0.4 kg
After you find the weight of the “other part”, you can use this information to find the weight of the melon if it only has 95% water. Since the “other part” does not evaporate (unlike water), the weight of it stays the same.
Weight of the other part (5% of the total weight): 0.4 kg
0.4 kg / total weight = 0.05
0.4 / 0.05 = total weight
8 kg = total weight