Problem 8 · 1998 AJHSME
Easy
Ratios, Rates & Proportions
rate
A child's wading pool contains 200 gallons of water. If water evaporates at the rate of 0.5 gallons per day and no other water is added or removed, how many gallons of water will be in the pool after 30 days?
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Answer: C — 185 gallons.
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Hint 1 of 2
A steady rate over a stretch of time means total change = rate × time. Find the whole amount lost before touching the 200.
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Hint 2 of 2
Once you know the total lost, the pool just starts at 200 and gives that much back.
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Approach: rate × time gives the total loss, then subtract
- Losing 0.5 gallon a day for 30 days is rate × time = 0.5 × 30 = 15 gallons gone.
- Starting from 200, that leaves 200 − 15 = 185 gallons.
- Trap check: the answer choices 198.5 and 199.85 are what you'd get if you forgot to multiply by all 30 days (subtracting only one day's loss, or mis-sliding the decimal). The phrase 'per day' for 30 days always means multiply first.
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