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Difference between revisions of "2017 AMC 10A Problems/Problem 9"

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==Solution==
 
==Solution==
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The distance from town A to town B is 10km uphill, and since Minnie rides uphill at a speed of 5 kph, it will take her 2 hour. Next, she will ride from town B to town C, a distance of 15 km all downhill. Since Minnie rides downhill at a speed of 30 kph, it will take her half(.5) of an hour. Finally, she rides from town c back to town a, a flat distance of 20 km. Minnie rides on a flat road at 20 kph, so this will take her 1 hour. Her entire trip takes her 3.5 hours.
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The distance from town <math>A</math> to town <math>B</math> is <math>10</math> km uphill, and since Minnie rides uphill at a speed of <math>5</math> kph, it will take her <math>2</math> hours. Next, she will ride from town <math>B</math> to town <math>C</math>, a distance of <math>15</math> km all downhill. Since Minnie rides downhill at a speed of <math>30</math> kph, it will take her half an hour. Finally, she rides from town <math>C</math> back to town <math>A</math>, a flat distance of <math>20</math> km. Minnie rides on a flat road at <math>20</math> kph, so this will take her <math>1</math> hour. Her entire trip takes her <math>3.5</math> hours.
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Secondly, Penny will go from town A to town C, a flat distance of 20km. Since penny rides on a flat road at 30 kph, it will take her two thirds(2/3) of an hour. Next Penny will go from town C to town B, which is uphill for Penny. Since penny rides at a speed of 10kph uphill, and town C and B are 15 km apart, it will take her one and a half(1.5) hours. Finally, Penny goes from Town B back to town A, a distance of 10km downhill. Since Penny rides downhill at 40 kph, it will only take her a quarter of an hour. In total, it takes her 29/12 hours, which simplifies to 2 hours and 25 minutes.
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Secondly, Penny will go from town <math>A</math> to town <math>C</math>, a flat distance of <math>20</math> km. Since penny rides on a flat road at <math>30</math> kph, it will take her <math>\frac{2}{3}</math> of an hour. Next Penny will go from town <math>C</math> to town <math>B</math>, which is uphill for Penny. Since penny rides at a speed of <math>10</math> kph uphill, and town <math>C</math> and <math>B</math> are <math>15</math> km apart, it will take her <math>1.5</math> hours. Finally, Penny goes from Town <math>B</math> back to town <math>A</math>, a distance of <math>10</math> km downhill. Since Penny rides downhill at <math>40</math> kph, it will only take her <math>\frac{1}{4}</math> of an hour. In total, it takes her <math>29/12</math> hours, which simplifies to <math>2</math> hours and <math>25</math> minutes.
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Finally, Penny's 2 Hour 25 Minute trip was 65 minutes less than Minnie's 3 Hour 30 Minute Trip
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Finally, Penny's <math>2</math> Hour <math>25</math> Minute trip was <math>65</math> minutes less than Minnie's <math>3</math> Hour <math>30</math> Minute Trip
  
 
==See Also==
 
==See Also==
 
{{AMC10 box|year=2017|ab=A|num-b=8|num-a=10}}
 
{{AMC10 box|year=2017|ab=A|num-b=8|num-a=10}}
 
{{MAA Notice}}
 
{{MAA Notice}}

Revision as of 17:54, 8 February 2017

Problem

Minnie rides on a flat road at $20$ kilometers per hour (kph), downhill at $30$ kph, and uphill at $5$ kph. Penny rides on a flat road at $30$ kph, downhill at $40$ kph, and uphill at $10$ kph. Minnie goes from town $A$ to town $B$, a distance of $10$ km all uphill, then from town $B$ to town $C$, a distance of $10$ km all uphill, then from town $B$ to town $C$, a distance of $15$ km all downhill, and then back to town $A$, a distance of $20$ km on the flat. Penny goes the other way around using the same route. How many more minutes does it take Minnie to complete the $45$-km ride than it takes Penny?

$\textbf{(A)}\ 45\qquad\textbf{(B)}\ 60\qquad\textbf{(C)}\ 65\qquad\textbf{(D)}\ 90\qquad\textbf{(E)}\ 95$

Solution

The distance from town $A$ to town $B$ is $10$ km uphill, and since Minnie rides uphill at a speed of $5$ kph, it will take her $2$ hours. Next, she will ride from town $B$ to town $C$, a distance of $15$ km all downhill. Since Minnie rides downhill at a speed of $30$ kph, it will take her half an hour. Finally, she rides from town $C$ back to town $A$, a flat distance of $20$ km. Minnie rides on a flat road at $20$ kph, so this will take her $1$ hour. Her entire trip takes her $3.5$ hours. Secondly, Penny will go from town $A$ to town $C$, a flat distance of $20$ km. Since penny rides on a flat road at $30$ kph, it will take her $\frac{2}{3}$ of an hour. Next Penny will go from town $C$ to town $B$, which is uphill for Penny. Since penny rides at a speed of $10$ kph uphill, and town $C$ and $B$ are $15$ km apart, it will take her $1.5$ hours. Finally, Penny goes from Town $B$ back to town $A$, a distance of $10$ km downhill. Since Penny rides downhill at $40$ kph, it will only take her $\frac{1}{4}$ of an hour. In total, it takes her $29/12$ hours, which simplifies to $2$ hours and $25$ minutes. Finally, Penny's $2$ Hour $25$ Minute trip was $65$ minutes less than Minnie's $3$ Hour $30$ Minute Trip

See Also

2017 AMC 10A (Problems • Answer Key • Resources)
Preceded by
Problem 8 		Followed by
Problem 10
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 • 21 • 22 • 23 • 24 • 25
All AMC 10 Problems and Solutions

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