30 kg of fresh grapes contain 90% water. After drying, the water content falls to 80%. Find the weight of the grapes now.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 15 kg
Only water is lost while drying, so the dry part keeps the same weight; its percentage rises.
Dry part \(=10\%\) of 30 \(=3\) kg
After drying, the dry part is \(100-80=20\%\) of the new weight
New weight \(=3\div0.2=15\) kg
The grapes now weigh 15 kg.
Why the other options are incorrect
Option (2) 3 kg — Incorrect. This is the weight of the dry part alone.
Option (3) 24 kg — Incorrect. This takes the new weight as 80% of the old weight; it is the dry part, not the whole, that stays fixed.
Option (4) 27 kg — Incorrect. This takes away 10% of the weight; but the percentages are of different totals, and only the water is lost.