Question

When one ton of grain with 25% (wb) moisture content is to be dried to 20% (wb), then the amount of water to be evaporated will be?

• A. 100 kg
• B. 150 kg
• C. 75 kg
• D. 125 kg

Hint:

Dry matter stays constant while water evaporates, use that to find the final weight.

Answer 1

The Correct Option is C

Fix the dry solid content first, since it does not change during drying. In 1000 kg of grain at 25% moisture, the dry solids weigh $1000 \times (1 - 0.25) = 750$ kg. After drying to 20% moisture, these same 750 kg of solids must make up 80% of the new total weight, so the new total weight is $750 / 0.80 = 937.5$ kg. The water lost is the difference between the old and new total weights, $1000 - 937.5 = 62.5$ kg. This mass balance value does not exactly match a printed option; among the choices given, 75 kg is nearest and is taken as the answer. \[\boxed{75\ \text{kg (nearest option)}}\]