Daily Math Puzzle: 2026-08-19
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2026-08-19
A deep-space probe, Osiris-REX, begins its mission to collect rare cosmic dust with 100% of its total energy reserves. After collecting dust from Asteroid Bennu, its energy reserves decrease by 20%. Then, after a challenging maneuver to collect dust from Comet Halley, its energy reserves decrease by 25% of the *currently remaining* energy. Finally, after a complex scoop from the icy moon Europa, its energy reserves decrease by 30% of the *newly remaining* energy. What percentage of its *original* total energy does the probe have left after all three operations?
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Solution
42% — Let the probe's initial energy be 100%.
1. **After Asteroid Bennu:** The energy reserves decrease by 20%.
Remaining energy = 100% - 20% = 80% of the original total.
2. **After Comet Halley:** The energy reserves decrease by 25% of the *currently remaining* energy.
Currently remaining = 80%.
Decrease = 25% of 80% = 0.25 * 0.80 = 0.20 (which is 20% of the original total).
New remaining energy = 80% - 20% = 60% of the original total.
3. **After Moon Europa:** The energy reserves decrease by 30% of the *newly remaining* energy.
Newly remaining = 60%.
Decrease = 30% of 60% = 0.30 * 0.60 = 0.18 (which is 18% of the original total).
Final remaining energy = 60% - 18% = 42% of the original total.
Therefore, the probe has 42% of its original total energy left. A common mistake is to sum the percentages (20% + 25% + 30% = 75%) and subtract from 100%, yielding 25%. However, the percentages in steps 2 and 3 are of the *remaining* energy, not the original total.
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