Problem 12 · 2020 Math Kangaroo
Medium
Ratios, Rates & Proportions
Fractions, Decimals & Percents
total-then-divide
Ana planned to walk an average of 5 km per day in March. In the first 10 days she walked an average of 4.4 km per day, and in the next 6 days she walked an average of 3.5 km per day. What average daily distance must she walk on the remaining days in order to fulfill her plan?
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Answer: C — 6 km
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Hint 1 of 2
March has 31 days; turn the planned average into a total distance she must cover.
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Hint 2 of 2
Subtract what she has already walked, then divide by the days that remain.
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Approach: work with totals over the month
- A 5 km average over 31 days means a target total of 5 × 31 = 155 km.
- First 10 days: 10 × 4.4 = 44 km; next 6 days: 6 × 3.5 = 21 km; so 65 km done in 16 days.
- Remaining distance 155 − 65 = 90 km over the last 15 days is 90 ÷ 15 = 6 km/day.
- The answer is 6 km, choice C.
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