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Rosie went on a hiking trip. The first day she walked 18 kilometers. Each day since, she walked 
90% of what she walked the day before.
What is the total distance Rosie has traveled by the end of the 
10^("th ") day?
Round your final answer to the nearest kilometer.

km

Rosie went on a hiking trip. The first day she walked 1818 kilometers. Each day since, she walked 90% 90 \% of what she walked the day before.\newlineWhat is the total distance Rosie has traveled by the end of the 10th  10^{\text {th }} day?\newlineRound your final answer to the nearest kilometer.\newlinekm \mathrm{km}

Full solution

Q. Rosie went on a hiking trip. The first day she walked 1818 kilometers. Each day since, she walked 90% 90 \% of what she walked the day before.\newlineWhat is the total distance Rosie has traveled by the end of the 10th  10^{\text {th }} day?\newlineRound your final answer to the nearest kilometer.\newlinekm \mathrm{km}
  1. Identify initial distance and decrease rate: Identify the initial distance walked and the daily decrease rate.\newlineRosie walked 1818 kilometers on the first day. Each subsequent day, she walked 90%90\% of the distance she walked the day before. This means there is a daily decrease rate of 10%10\% (100%90%100\% - 90\%).
  2. Calculate distance on second day: Calculate the distance walked on the second day.\newlineTo find the distance walked on the second day, multiply the first day's distance by 9090%.\newlineDistance on second day = 18km×90%=18km×0.9=16.2km18 \, \text{km} \times 90\% = 18 \, \text{km} \times 0.9 = 16.2 \, \text{km}
  3. Recognize pattern of distance walked: Recognize the pattern of distance walked each day.\newlineThe distance walked each day forms a geometric sequence where the first term is 18km18\,\text{km} and the common ratio is 0.90.9 (90%90\% of the previous day).
  4. Use formula for sum of geometric sequence: Use the formula for the sum of the first nn terms of a geometric sequence to calculate the total distance.\newlineThe sum of the first nn terms of a geometric sequence is given by Sn=a(1rn)/(1r)S_n = a \cdot \left(1 - r^n\right) / \left(1 - r\right), where aa is the first term, rr is the common ratio, and nn is the number of terms.
  5. Calculate total distance on 1010th day: Calculate the total distance walked by the end of the 1010th day.\newlineUsing the formula from Step 44, with a=18a = 18 km, r=0.9r = 0.9, and n=10n = 10:\newlineS10=18×(10.910)/(10.9)S_{10} = 18 \times (1 - 0.9^{10}) / (1 - 0.9)
  6. Perform calculations: Perform the calculations.\newlineS10=18×(10.910)/(10.9)S_{10} = 18 \times (1 - 0.9^{10}) / (1 - 0.9)\newlineS10=18×(1(0.910))/0.1S_{10} = 18 \times (1 - (0.9^{10})) / 0.1\newlineFirst, calculate 0.9100.9^{10}:\newline0.9100.34870.9^{10} \approx 0.3487\newlineNow, substitute this value into the formula:\newlineS10=18×(10.3487)/0.1S_{10} = 18 \times (1 - 0.3487) / 0.1\newlineS10=18×0.6513/0.1S_{10} = 18 \times 0.6513 / 0.1\newlineS10=11.7234/0.1S_{10} = 11.7234 / 0.1\newlineS10=117.234S_{10} = 117.234
  7. Round final answer: Round the final answer to the nearest kilometer.\newlineS10117S_{10} \approx 117 kilometers

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