The Flight Of Smaug

Algebra Level 3

Gandalf is riding on Shadowfax away from The Lonely Mountain at 8 leagues per hour and his heading toward Dol Guldur. At the exact same time, Radagast is riding toward Gandalf from Dol Guldur on his Rhosgobel rabbits at a pace of 6 leagues per hour. The distance between The Lonely Mountain and Dol Guldur is 1890 leagues. Smaug also leaves The Lonely Mountain at the same time Gandalf does, and he flies toward Radagast. When he reaches Radagast, he suddenly turns around and flies back to the approaching Gandalf. Then, when he reaches Gandalf, he turns back and flies toward the nearing Radagast. He repeats this, at a speed of 17 leagues per hour, until Gandalf and Radagast finally meet. The number of leagues Smaug has flown is equal to X. What is X divided by 5?


The answer is 459.

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30 solutions

Trevor B.
Jan 1, 2014

We could go at this by trying to find directly how far Smaug flew by calculating the sum of an infinite geometric sequence, but that might be a little tricky considering the ugly numbers in the problem. Instead, we can find the amount of time it takes Gandalf and Radagast to reach each other and multiply it by how fast Smaug travels, using the equation d = s × t d=s\times t (distance = = speed × \times time).

Gandalf and Radagast are traveling at each other at a relative speed of 14 14 leagues per hour. We can treat this problem as Gandalf riding at 14 14 leagues per hour towards a stationary Radagast. It would take Gandalf 1890 14 = 135 \frac{1890}{14}=135 hours to reach Radagast. In this time, Smaug will have traveled X = 135 × 17 X=135\times17 leagues.

X 5 = 135 × 17 5 = 27 × 17 = 459 \frac{X}{5}=\frac{135\times17}{5}=27\times17=\boxed{459}

I applaud these characters on their abilities to not sleep for more than 5 5 days.

Welcome to Hollywood, my friend. :P

Josh Petrin - 7 years, 5 months ago

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I hope they can do without a bathroom for 5 days

Santanu Banerjee - 7 years, 5 months ago

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I hope they can do it like cows.

Daniel Wang - 7 years, 5 months ago

Your solution is nice. But even without invoking the Physics of 'travelling Frames of References', we can do away with extraneous calculation by just assuming a time t the two riders take to meet. Multiply the time with the respective speeds of riders and equate that to the distance between the Mountain and Dol Guldur. And then solve for t .

Now I am just figuring out how to use my map of the Shire in the problem.

Wamiq Reyaz - 7 years, 5 months ago

There was a slight ambiguity...as to where Radagast started from...I corrected it several times....but then forgot to actually change it at the last correction. It should say Radagast started from Dol Guldur My apologies to anyone that was confused! :)

Asher Joy - 7 years, 5 months ago

Can you show me how to solve this using an infinite geometric sequence?

Kenneth Wang - 7 years, 5 months ago

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It is actually a lot harder with infinite geometric sequences. Just solving for t and multiplying it by 17 is a lot faster and simpler.

Asher Joy - 7 years, 5 months ago

last line was super :)

Akram Mohiddin - 7 years, 4 months ago
Raj Magesh
Jan 2, 2014

This is actually remarkably simple, once you think about it. There is a slight ambiguity in the question for readers unfamiliar with Tolkien: Radagast is approaching Dumbledore from Dol Guldur, which means they are moving towards each other along a straight line!

Now, consider the time taken for Gandalf and Radagast to meet:

1890 ÷ ( 6 + 8 ) = 135 1890 \div (6+8) = 135

Since the time taken for them to meet is 135 hours, Smaug has also been flying for 135 hours! But note that Smaug is flying at a constant speed of 17 leagues per hour...

Hence, the distance travelled by Smaug is:

135 × 17 = 2295 2295 ÷ 5 = 459 135 \times 17 = 2295 \Longrightarrow 2295 \div 5 = \boxed{459}

Well now things get really interesting if you subscribe to the theory that Middle Earth is based on Europe at the time it was written...So assuming this idea is true: Dumbledore would start from Hogwarts which we know to be near Dufftown and Radagast would still start from Dol Guldur. If Dol Guldur is 1890 leagues from the Lonely Mountain, that translates into roughly 400 miles. The distance from Dufftown to my best approximation of Dol Guldur is 865 miles or 4087 leagues. So, based on the speed of Harry's fastest broomstick, Dumbledore could fly at 150 mph or 708.25 leagues per hour.

Therefore we do 4087/(708.25+6)=5.722 hours

Now we multiply by 17 and divide by 5 for a new answer of 19.45

Sorry couldn't resist :)

Sources: http://i24.photobucket.com/albums/c18/maxphotouk/middleearth3.jpg

http://en.wikibooks.orgwiki/Muggles%27 Guide to Harry Potter/Magic/Brooms

http://www.daftlogic.com/projects-google-maps-distance-calculator.htm

A Former Brilliant Member - 7 years, 5 months ago

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Oh damn. I just noticed the gaffe in my solution. I meant Gandalf, not Dumbledore. Hehe. Twiddles thumbs

Raj Magesh - 7 years, 5 months ago

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Yeah I figured you did but I couldn't resist. Hope you didn't mind too much...

A Former Brilliant Member - 7 years, 5 months ago

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@A Former Brilliant Member Haha, no, not at all! I always liked Harry Potter more than LOTR, though.

Raj Magesh - 7 years, 5 months ago

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@Raj Magesh Well it could easily be rewritten with broomsticks and snitches if you were so inclined...

A Former Brilliant Member - 7 years, 5 months ago

Wait...where did you get Dumbledore from?

Asher Joy - 7 years, 5 months ago

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He Apparated into my solution after persuading Gandalf to eat his poisoned lemon drops. Couldn't get him away. Sorry :\

Raj Magesh - 7 years, 5 months ago

Dumbledore? Gandalf, you mean?

Vivek Bhupatiraju - 7 years, 5 months ago

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Gandalf is nothing compared to Dumbledore, the Headmaster of Hogwarts, Defeater of Grindelwald, Leader of the Light, Chief Warlock of the Wizengamot and the Supreme Mugwump of the International Confederation of Wizards!

But yeah, you're right. My mistake. XD

Raj Magesh - 7 years, 5 months ago
Anuj Mishra
Jan 2, 2014

Time taken by Gandalf to meet Radagast = 1890/(8+6)=135hrs Through this whole time Smaug was moving at the speed of 17 lgs/hr. So distance that smaug travels,X=17*135=2295 leagues Thus, X/5=459 Ans.

Rahman 007
Jan 2, 2014

This is a pretty easy problem but the description is too complex..... just think Gandalf and Radagast run 8+6=14 leauges per hour.... so total 1890/14=135 hours of running. In this period Smaug fly at 17 leagues per hour. so answer is 17*135/5=459. Hope this helps... Thank you.

Ashwin K
Feb 2, 2016

I can give a shortcut which seems to be amazing for this lengthy problem.

In this problem, we see time remains constant,

i.e. The time taken by Gandalf & Radagast to meet each other riding in opposite direction is same as the Smaug riding in this entire duration.

We know that when time remains constant ,

Distance is directly proportional to Speed which means that the speed ratio is same as
the distance ratio and are directly related.

speeds of (Gandalf(8) + Radagast(6)) and Smaug can be related,

 14:17

which is same as their distance ratio.

The distance 1890 leagues must have been covered by (Gandalf + Radagast) .

In this time, Distance covered by Smaug = (1890/14)*17 = 2295.

X = **2295**.

X/5 = **459**.//
Akram Mohiddin
Feb 7, 2014

Gandalf and radagast are approaching each other(opposite direction) with speed 8=6=14 leagues/hr total distance=1890 leagues so time taken by them to meet=1890/14=135 hrs IMPORTANT: for 135 hrs Smaug should be running back and forth continuously.So, his total distance traveled X= 135 x 17 =2295 leagues x/5=459

Dfsfsf Rertert
Feb 3, 2014

total speed = 14 kmph. Time at which they meet each other = 1890/14,and that is when Smaug stops. Distance = speed time taken = (1890/14) 17=2295 = X.X/5 = 459

Muhammad Jahangir
Jan 24, 2014

As Radaghast and Gandalf are moving towards each other so the 1890 leagues / ( the sum of there speeds) gives us the time they ll meet I.e 135 hrs. Now multiply that with the speed of smaug and VOLA we have the distance travelled by smaug, X= 2295. And X/5 = 459

Liam Ashby
Jan 23, 2014

The combined velocity of Gandalf and Radagast is 14 l/hr so it takes them 135 (1890/14) hours to meet since Time = Distance / Velocty. In that time Smaug flies at 17//hr (assuming changes of direction are instantaneous) therfore covers 17*135 leagues (since Distance = Velocity * time). X= 2295. X/5 = 459

Lokesh Gupta
Jan 20, 2014

Time for Gandalf and Radagast to meet= 1890/(8+6)= 135 hours. All this while, Smaug is flying to and fro between them at a speed of 17. So, leagues flown by Smaug, X=135x17.

X/5=135x17/5=459

Statement : Gandalf & Radagast are riding towards each other at 8 and 6 leagues per hour respectively. Hence if we calculate the relative speed its 14 leagues per hour (8+6),

So to cover the distance of 1890 leagues they would require = 1890/14 = 135 hours. In 135 hours Smaug who is flying back and forth at 17 leagues/ hr. will cover 17*135 = 2295 leagues = X

X/5 = 459

Dhruv1008 Agarwal
Jan 17, 2014

speed of gandalf is 8leagues/h speed of radagast is 6leagues/h as they are approaching each other therefore speed adds up hence net speed is 14leagues/h distance is 1890 therefore time is 1890/14=135 hours distance travelled by smaug is 135*17 after dividing by 5 we get 459

Vivek Pant
Jan 16, 2014

Well I have used a little bit of physics here Let the distance travelled by Gandalf be x ,distance covered by Radagast will be 1890-x (x is the distance at which they meet) Let the time taken by them for meeting each other be t.

Now for Gandalf. x÷t=8.
x=8t.
(Distance ÷time= speed) For Radagast.
1890-x ÷t = 6 1890-x = 6t 1890 - 8t = 6t 14t=1890 t= 135


Now the total distance travelled by samug in 135 hrs = 135 × 17 = 2295 Therefore. 2295÷5 = 459

Ahmad Awalluddin
Jan 16, 2014

This question was totally easy. First we need to ignore how much time the smaug turns.

The most important is to find how much time did Gandalf and Radagast to meet.

so x(8+6)=1890 x=135 the number of leauge/135=17

hence the number of leauge =2295 2295*5=459

Anubhav Bhatt
Jan 15, 2014

total time taken for gandalf and radagast to be at the same position = 1890/(8+6)=135hrs. number of leagues covered by Smaug = X = 135*17=2295. X/5=459.

Karim Magar
Jan 13, 2014

let Gandalf=Y , Radagast=Z & Smaug=X First X+Y=1890 , Y=(4/3)Z , (7/3)Z=1890 , Z=810 leagues & Y=1080 The time elapsed = (1080/6)=135 Hours the time elapsed for X for one shoot = (1890/17)=111.1764 Hours then the total leagues for X=(135/(1890/17))*1890=2295 leagues divided by 5 = 459 leagues

After setting out from their respective locations Gandalf & Radagast met after 1890/(8+6)=135 Hours. At the same time Smaug travelled 17 X 135 leagues. So Ans (17 X 135)/5=459.

Jeremi Litarowicz
Jan 12, 2014

From Gandalf's perspective, Radagast is traveling at 8 + 6 = 14 8+6=14 leagues per hour towards him. This means that it will take him 1890 / 14 = 135 1890/14=135 hours to reach Gandalf. During this time, Smaug was traveling at a constant 17 leagues per hour, thus traveling 135 × 17 = 2295 135 \times 17=2295 leagues. This is our desired quantity X X , and one fifth of it is 459 \boxed{459} leagues.

Arpit Sah
Jan 12, 2014

Distance covered by Gandalf in 1 hour = 8 leagues

Distance covered by Radagast in 1 hour = 6 leagues

therefore, distance covered by them in 1 hour = 8 + 6 = 14 leagues

Time taken for them to meet each other = 1890 14 \frac{1890}{14}

Therefore, Time taken for them to meet each other = 135 hours

X = 135 × 17 135 \times 17 league

X divided by 5 = 27 × 17 27 \times 17 = 459

Jaiman Singh Gill
Jan 11, 2014

Best problem i've seen on here. Total distance = 1890 leagues. Radagast-Gandalf combined pace=14 LPH. Take Dol Guldor as starting place and say radagast's pace is 6 LPH and a fraction of total pace is 6/14 so total distance of Gandalf/Radagast meeting spot (from Dol Guldur) is (6/14)x1890 which gives a distance of 810 L from Dol guldur. And using T=D/S sub in values of radagasts speed of 6LPH and distance of 810L and get 135 hours of total travel time. As smaug stops flying back and forth when the 2 wizards meet (after 135 hours). Smaug is flying for 135 hours. then use smaug's pace of 17LPH in the equation D=SxT to get a total distance of 2295L for X. X/5=459. Answer=459

Punarva Katte
Jan 10, 2014

Firstly, we need to assume that Radagast starts from Dol Guldur (not mentioned in the problem).

Lets say the time taken for Gandalf and Radagast to meet is 'T' hours. Then, 8 T+6 T = 1890, T = 135 hours

Smaug may be flying back and forth, but since he/she is flying at constant speed and distance covered in 'T' hours is, D = 17*T = 2295 leagues

(D/5) =459, which is the answer to this question.

Rohit Chalasani
Jan 8, 2014

The distance between The Lonely Mountain and Dol Guldur is 1890 leagues. The relative velocity of Gandalf and Radagast is 14 leagues per hour (8+6). Thus Gandalf and Radagast would meet after 1890/14 = 135 hours. In 135 hours, Smaug would travel 135*17 leagues, which is equal to X. Hence, X/5 equals 459.

Anis Abboud
Jan 6, 2014

Gandalf and Dol Guldur are 1890 1890 leagues away, and are approaching each other with a combined speed of 8 + 6 = 14 8 + 6 = 14 leagues per hour. So they will meet after 1890 / 14 = 135 1890/14 = 135 hours.

Hence, Smaug will fly 135 135 hours with a speed of 17 17 leagues per hour. So he will fly 135 17 = 2295 135 \cdot 17=2295 leagues.

So the answer is 2295 / 5 = 459 2295/5 = \boxed{459} .

Ajit Athle
Jan 5, 2014

Distance between the two points=1890, Speed of Approach = (8+6)=14 L/Hr. Hence time taken to meet =1890/14 = 135 hrs. So distance travelled by Smaug, X = 135*17 = 2295 L. Reqd. Ans =2295/5 = 459. (This is yet another unnecessarily complicated version, if I may say so, of the bird flitting between two approaching trains attributed to Von Neumann)

You can approach the problem by solving the time needed for Gandalf and Radagast to meet then multiplying to the speed of Smaug to get the total distance traveled.

With this, we could calculate that Gandal and Radagast are nearing each other at the rate of their combined speeds (8 + 6) = 14 Leagues per hour. The total distance in between is 1890 leagues. We then get the time needed by dividing the speed to the total distance (1890/14) = 135 Hours From this we multiply the speed of Smaug of 17 leagues per hour = 2295 leagues. Finally to get the number asked we divide it by 5 and we get 459.

Samik Banerjee
Jan 3, 2014

Total Distance = 1890 Leagues. Time Taken for Gandalf & Radagast to meet = 1890 / ( 8 + 6 ) Hrs. Total League crossed in that time by Smaug = ( 1890 / ( 8 + 6 ) ) * 17 Leagues = X

Aashrit Raj
Jan 2, 2014

As Smaug continues the rounds until Gandalf and Radagast meet,first calculate the time taken for them to meet which will be 1890/(8+6)=135hrs. Multiplying the time taken with Smaug's speed we get 2295leagues as the total distance traveled by Smaug. And 2295/5=459.

Edmund Heng
Jan 2, 2014

To find the number of leagues that Smaug has travelled, we need to find the total time needed for Gandalf and Radagast to meet, so

Number of hours = 1890 8 + 6 \frac{1890}{8+6} = 135 X = 17 × 135 = 2295 \Rightarrow X = 17 \times 135 = 2295

A Joshi
Jan 2, 2014

Time required for Radagast and Gandalf to meet = distance / relative speed = 1890 / (8+ 6) =135 hours Therefore distance covered by Smaug till these two meet = 135*17 Therefore X/5=135 * 17/5 =459

Oindrila Ghosh
Jan 2, 2014

the relative speed of gandalf and radagast is (8+6)=14L/hr..(since they r approaching towards each other).. so they will mt after 1890/14 =135hrs.. the speed of smaug is 17L/hr . so the distance it can cvr in 135hrs is 135 17L=X(given) so X/5=135 17/5=459...

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