Problem 23 · 2024 Math Kangaroo
Stretch
Fractions, Decimals & Percents
percent-multiplier
Fresh mushrooms consist of 80% water. In dried mushrooms, however, the water is only 20% of the mass. By what percentage does the mass of a mushroom decrease during drying?
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Answer: C — 75
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Hint 1 of 2
The dry solid part of the mushroom never changes when water leaves; only water mass drops.
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Hint 2 of 2
Track the solid mass: it is 20% before and 80% after, so set up the new total from the fixed solid.
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Approach: hold the solid mass fixed and find the new total
- Take 100 g fresh: 80% water means 20 g of solid.
- Dried, water is 20% so solid is 80% of the new mass: 20 = 0.8 × new, giving new = 25 g.
- Mass drops from 100 g to 25 g, a decrease of 75%.
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