Latest Book Aptitude Question SOLUTION: There are 49 students in a class.Kiran told that sum of all roll numbers below his number and after his number are equal.find the roll number of kiran

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(#M40010777) BOOK question roll number Keep an EYE

There are 49 students in a class.Kiran told that sum of all roll numbers below his number and after his number are equal.find the roll number of kiran

Asked In Book jomon v j (11 years ago)

Solved sainath Read Solution (6)

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Read Solution (6) :

sainath  (11 years ago)

the roll number of kiran is 35...
suppose n+1 is kiran's roll number
sum of roll's above kiran=n(n+1)/2 [sum of n natural numbers]
sum of roll's below kiran=[49(50)/2]-[(n+1)(n+2)/2]
[sum of numbers upto 49 - sum of numbers up to kiran's roll num(n+1)]
=>n(n+1)/2=[49(50)/2)-[(n+1)(n+2)/2]
=>n(n+1)+(n+1)(n+2)=49(50)[take n+1 common on lhs]
=>(n+1)(2n+2)=49(50)
=>(n+1)(n+1)=49(25) [dividing by 2 on both sides]
=>n+1=7(5) [squre root]
=>n=34

so, kiran's roll number is n+1=35...

Is this solution Helpfull? Yes (8) | No (4)  

Arijit Mandal  (11 years ago)

total sum of roll number=49(49+1)/2=1225
let kiran's roll num=x;
student before her=x-1;
student after her=49-x;
total sum of ages of x-1 student=(x-1)(x-1+1)/2=x(x-1)/2;
so,x(x-1)/2=(1225-x)/2
=>x^2-x=1225-x
=>x=sqrt(1225)
=>x=35
kiran's rol=35

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K.V.Hariprasath  (11 years ago)

simply answer is 35...i too agree...but technique i found is
step 1)by calculating sum of natural numbers(here 49) gives total value(1225)..
step2)calculate square root of tat number gives you answer..so in general its to find sum and take square of tat number gives you exact or approxiamte answer

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jomon v j  (11 years ago)

dear Pragkarma ,it is given that sum of roll numbers below after are equal .your answer is wrong

Is this solution Helpfull? Yes (2) | No (1)  

PARAG KAMRA  (11 years ago)

the roll number of kiran is 25,because above and below are 24(equal)
25(ans)

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Sumit Biswas  (11 years ago)

didnt get the question!

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