Raj and Vikram's Travels

Algebra Level 2

Raj and Vikram are two travelers in ancient India, walking along the Silk road. On the first day of travel, Raj travels 5 5 yojanas, and on each successive day travels 3 3 yojanas more than the previous day. Vikram started at the same place and travels the same path, but started 5 5 days earlier, and travels 7 7 yojanas a day. On which day of Raj's travel will the two of them meet?

Details and assumptions

A yojana is an ancient Indian unit of measure.

The silk road does not cross itself. Rai and Vikram will meet only if they have travelled the same distance.

If they meet at any point on the 123rd day (say at 12:34pm), then your answer is that they meet on the 123rd day.


The answer is 7.

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13 solutions

Daniel Chiu
Dec 8, 2013

By day d d , Vikram has traveled 35 yojanas already, and 5 d 5d more.

Raj has traveled 5 + 8 + 11 + + ( 5 + 3 ( d 1 ) ) 5+8+11+\cdots+(5+3(d-1)) . The average distance for each day is 10 + 3 ( d 1 ) 2 \dfrac{10+3(d-1)}{2} , and so Raj's total distance is d 2 ( 10 + 3 ( d 1 ) ) \dfrac{d}{2}(10+3(d-1)) .

Then, we equate the two. 35 + 7 d = d 2 ( 10 + 3 ( d 1 ) ) 35+7d=\dfrac{d}{2}(10+3(d-1)) Expanding, 35 + 7 d = 5 d + 3 d ( d 1 ) 2 35+7d=5d+\dfrac{3d(d-1)}{2} Clearing the fraction, 70 + 14 d = 10 d + 3 d ( d 1 ) 70+14d=10d+3d(d-1) Moving all terms to one side, 3 d 2 7 d 70 = 0 3d^2-7d-70=0 By the quadratic formula, the positive solution to this is 7 + 7 2 + 4 ( 3 ) ( 70 ) 6 = 7 + 889 6 \dfrac{7+\sqrt{7^2+4(3)(70)}}{6}=\dfrac{7+\sqrt{889}}{6} Since 889 \sqrt{889} is a little less than 30, 7 + 889 6 37 6 \dfrac{7+\sqrt{889}}{6}\approx\dfrac{37}{6} which is slightly more than 6 days. By the last assumption, the answer is 7 \boxed{7} .

Raj 5,13,24,38,55,75,98 Vikram 7,14,21,28,35,42,49,56,63,70,77,84,91,98

On Raj travelled 7th day, he met Vikram

Zabiero See - 7 years, 6 months ago

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for the 1st day its 5 and here it's mention that next day will walk 3 more so 5+3=8 and what you did here 5, 5+8=13 so ( 5,13 ans so on ? )

Satish Kumar - 7 years, 6 months ago

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successive day(next day) increases by 3. i.e 3+ previous day so.. 1st day= 5 2nd day= 5+3=8 3rd day= 8+3 =11

Kavi Sro - 7 years, 6 months ago

hahaha.

Alvin Reyes - 7 years, 6 months ago

Distance(Day) for Vikram 7(1), 14(2), 21(3), 28(4), 35(5), 42(6), 49(7), 56(8), 63(9), 70(10), 77(11), for Raj 5(5), 13(6), 24(7), 38(8), 55(9) , 75(10) , 98(11) , 124(12)

Yuliya Skripchenko - 7 years, 6 months ago

(5+5+(x-1)3)x/2 = 35 + 7x

(10 +3x-3)x/2= 35 + 7x

(7 + 3x)x/2= 35 + 7x

That's what I was thinkin'

Sinuhé Ancelmo - 7 years, 6 months ago

thank you

Vinay Jain - 7 years, 6 months ago

Small typo : You mean to say 7d more in the first line?, Otherwise excellent solution.

A Former Brilliant Member - 7 years, 6 months ago

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Yep, you are correct!

Daniel Chiu - 7 years, 6 months ago

thank you

Wesley Davesh - 7 years, 6 months ago

Nice solution!!!!!

Yao Feng Ooi - 7 years, 6 months ago

nice

Kashif Rajput - 7 years, 5 months ago

is there another solution?

roella dumos - 7 years, 6 months ago

Rai Vikran 0 35 yojanas on the 5th day 5 42 6th day 13 48 7th day 24 56 8th day 38 63 9th day 55 70 10th day 75 77 11th day 98 84 12th day So as Rai is supposed to pas Vikran on the 12th day we have to calculate the number of unsuccessful days Rai had in his trip as 12-the number of days=the day of the meeting and it comes by calculating the distance between them on the 12th day 98-84=14 yojanas,and by dividing it by 3 we will have 4 days 16 hours so 12-4D 16H=7D 8H and the meeting is on the 7th day,08:00 AM

AlHasan Sameh - 7 years, 6 months ago

before day 1 Vikram traveled (7*5) 35 yojanas. On the particular day this additional 35 yojanas will be zero, they will meet. so Raj (-2+1+4+7+10+13+..). on 7th day they will travel sme distance.

Mohammad Mohiuddin Bhuiyan - 7 years, 6 months ago

7th day...

siva prakash - 7 years, 6 months ago

I just typed a random answer.. I got it right! Lucky guess \m/

Cedric Olita - 7 years, 6 months ago

I got slightly wrong, I answered 6, and when it showed I was wrong I tried to see the solutions. But now I can't proceed. Any help? I am new here.

Kryon Krenoteve - 7 years, 6 months ago

huge equation O.o

Kinnor Luba - 7 years, 6 months ago
Rishi Kanaujia
Dec 9, 2013

Let n be the no. of Raj's day at which Raj meets Vikram. Now, Raj travels in an arithmetic progressive pattern. Sum of this arithmetic progression and equating with Vikram's no. of yojanas should give the answer. n/2 {2 5+(n-1)3}=7(n+5)

solving this, we get the value of n as 7.

Sn= n/2(2a+(n-1)d) and here a is 5 and AP will be 5,8,11 so 2*a=10 here from where did you put values and made it 25 ?

Satish Kumar - 7 years, 6 months ago

good job .. great

Reymond Adelfa - 7 years, 6 months ago

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aww..i did some silly mistake..

Trish Destiny - 7 years, 6 months ago

ohh no i did the same bthere was a silly calculation problem:P

Somveer Jaat - 7 years, 6 months ago

how do yuo get 25???

Sukrut Waghmare - 7 years, 6 months ago
Krishna Chaitanya
Dec 10, 2013

(Raj-5 day delay ) # # # # # 5 , 8 , 11 ,14 , 17 , 20 =total (75)

(vikram5 dy erly) 7 7 7 7 7 7 7 7 7 7 7 = (77)

by 6th day RAJ, covered total of 75 yojana and vikram total of 77 , so on the 7th day of raj , raj will meet vikram

7th day

Please show mathematically?

Shubham Thakkar - 7 years, 6 months ago

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Who didn' show mathematically?

Sinuhé Ancelmo - 7 years, 6 months ago

how the ans is 7???????////

Mudaser Khosa - 7 years, 6 months ago

Can you explain your thinking step by step?

Calvin Lin Staff - 7 years, 6 months ago
Daniel Alfaro
Dec 13, 2013

Lets say d is the distance travelled and t is time. Since we are in Raj´s time Domain, Vickram will have travelled 35 yojanas(Y) in t=0, so what we have to do is find both equations and find their intersection. We can do it graphically, but it will be hard. So lets do it analytically:

Vickram: d v = 7 t + 35 d_v=7t+35

Rajs: it goes like this, 5+8+11+14... which is an arithmetic progression, so the sum and therefore d will be: d = a 0 + a n 2 n d r = 5 + ( 5 + ( t 1 ) 3 2 t = 7 t + 3 t 2 2 d=\frac{a_0+a_n}{2}\cdot n\longrightarrow d_r= \frac{5+(5+(t-1)3}{2}\cdot t=\frac{7t+3t^2}{2}

d v = d r 7 t + 3 t 2 2 = 7 t + 35 3 x 2 7 x 70 = 0 d_v=d_r \longrightarrow \frac{7t+3t^2}{2}=7t+35 \longrightarrow 3x^2-7x-70=0

so we solve this equation: t = 7 + 49 + 840 6 = 7 6 + 889 6 1 + 30 6 6 t= \frac{7+\sqrt{49+840}}{6}=\frac{7}{6}+\frac{\sqrt{889}}{6}\approx 1+\frac {30}{6}\approx 6

since 7 6 + 889 6 \frac{7}{6}+\frac{\sqrt{889}}{6} is a bit higher than 6 our t is slightly higher than 6 so it will be in the beginning of the 7 day that they will meet

7=t

Vikram=7 t+35 ;t is the days of Raj's travel. The way Raj travels gives an idea of arithmetic series Raj=(t/2)(10+3 t) equating the two equations gives t=6.1... so t=7

Venture Hi
Feb 13, 2014

There will never be enough poratas for one yojana....lol http://www.youtube.com/watch?v=8_ABBgJWUPM&list=LLAQYzkrnAS1yM2aWR5W6cmg

Aditya Joshi
Feb 11, 2014

Let Raj take t t days to reach the place where they meet. Therefore, Vikram takes t + 5 t + 5 days.

Now, we know that distance = speed × time \text{distance} = \text{speed} \times \text{time} .

Thus, distance traveled by Vikram to meet at the common place is 7 ( t + 5 ) 7(t+5) .

We have to find the distance traveled by Raj to reach this place.

Now, Raj travels 5 5 yojanas on the first day, 8 8 on the second day and so on. We need to sum these up till day t t to get the total distance traveled till day t t .

First, we need a closed form of the distance traveled by Raj on the t th t^{\text{th}} day. That is the recurrence

p ( t ) = 3 + p ( t 1 ) p(t) = 3 + p(t-1) and p ( 1 ) = 5 p(1) = 5

Solving this, we get p ( t ) = 3 t + 2 p(t) = 3t + 2 . Therefore, he has traveled

t = 1 t 3 t + 2 \displaystyle\sum\limits_{t=1}^t 3t + 2 yojanas in t t days. The closed form for this is 1 2 t ( 7 + 3 t ) \dfrac{1}{2} t(7 + 3t)

Thus, we equate

1 2 t ( 7 + 3 t ) = 7 ( t + 5 ) \dfrac{1}{2} t(7 + 3t) = 7(t+5)

Solving this, we get the positive root of t t at

t = 1 6 ( 7 + 889 ) 6.1360 t = \dfrac{1}{6} (7 + \sqrt{889}) \approx 6.1360 days so he reaches on the 7 th 7^{\text{th}} day.

Aditya Karekatte
Dec 15, 2013

The total distance in yojanas travelled by Raj on the 'n'th day of his travel is given by: \frac{n}{2} \times (2a + (n-1)d)

On the 'n'th day of Raj's travel, Vikram has travelled: 35 + 7n yojanas.

Equating the two and solving, we get: n = 6.136, -3.802

*Since the answer cannot be negative, and the 6.136th day is a part of the 7th day, the answer is * 7

i can not undertstand,please give details

sukriti kundu - 7 years, 3 months ago
Shrinand Thakkar
Dec 13, 2013

Day. Vikram dis. Raj distance 1. 42 5 2. 49 13 3. 56 24 4. 63 38 5. 70 55 6. 77 75

on 7th day they would meet

Ritesh Pahwani
Dec 13, 2013

As Vikram travels 7 Yojans a day ,Then we will have to find the amount of yojans that Raj has travelled which is divisible by 7,,so on 1st day Raj travels 5 Yojans..on 2nd day he travels 3 more than previous ones means 3+5=8..on 3rd day still three more means 8+3=11 and this continues and on the 7th day the equation becomes 75+23=98 which is divisible by 7 and on that day it will become 14th day of vikram's Travel..:) Hope you find it quite usefull

35+7n = 5+ 3((n-1)n/2). Got n^2-(16/3)n-20=0. Asked Wolfram alpha to simplify it and it showed me a graph which had 7.8735 as one of the roots.

Arpan Sinha
Dec 10, 2013

use the formulas for sum of an arithmetic progression and

n=n'+4.......;where n and n' are no of days for raju and vikram resp. n'=1,2,3....

can you describe your this opinion?

পিটার প্যান - 7 years, 6 months ago

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