Latest Elitmus Aptitude Question SOLUTION: There are 7880 ball of radius 1 cm, if the ball are arranged in a form of pile such that top has 1 ball,2nd layer has 3,3rd has 6,4th has 10,5 has 10 and so on.how many levels are

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(#M40036490) ELITMUS Numerical Ability question Keep an EYE

There are 7880 ball of radius 1 cm, if the ball are arranged in a form of pile such that top has 1 ball,2nd layer has 3,3rd has 6,4th has 10,5 has 10 and so on.how many levels are there.
Option
a. 33
b. 32
c. 34
d. 31

Asked In Elitmus deepkamal (10 years ago)

Unsolved Read Solution (6)

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Read Solution (6) :

Manu   (10 years ago)

The ques should be 1 ball at 1st layer, 3 at 2nd , 6 at 3rd , 10 at 4th, 15 at 5th ....... Then the series will become 1,3,6,10,15,21 ..... so on . Now taking first and second term together it will add up to 4 next two to 16, next two to 36 next two to 64 and so on. Den series will become 4,16,36,64, ... Take 4 common 4 (1+2*2+3*3+4*4 .....)
So 7880=4(1+2*2+3*3+4*4 .....)
7880*3/2=(N)(N+1)(2N+1)

Is this solution Helpfull? Yes (5) | No (1)  

naveen  (10 years ago)

34
as it is in the form of n*(n+1)/2
equation is n*(n+1)/2+n*(n+1)(2n+1)/6=7880
it gives u n=34

Is this solution Helpfull? Yes (2) | No (11)  

Soma Ghosh  (10 years ago)

how did u gt n*(n+1)/2+n*(n+1)(2n+1)/6=7880 ???

Is this solution Helpfull? Yes (2) | No   

deepak kumar  (10 years ago)

1+3+6+10....n term
sum=n(n+1)(n+2)/6
hene n=34

Is this solution Helpfull? Yes (1) | No (6)  

Anurag patel  (7 years ago)

n(n+1)(n+2)/6=9880

ans -38

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Agniv Chatterjee  (9 years ago)

@Manu Please Explain More :/

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