Latest self Aptitude Question SOLUTION: what is 87th term in the given series: 2,10,26,50

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what is 87th term in the given series:
2,10,26,50

thrishul (11 years ago)

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Saurabh Awasthi  (11 years ago)

Observing the given we can write the following :


2nd term - 1st term = 1*8;
3rd term - 2nd term = 2*8;
4th term - 3rd term = 3*8;
5th term - 4th term = 4*8;
.
.
.
(n-1)th term - (n-2)th term =(n-2)*8
(n)th term - (n-1)th term =(n-1)*8;
---------------------------------------------
Summing up all the above terms we get ,
(n)th term - 1st term = {1+2+......+(n-1)}*8
=>(n)th term = 8*{n*(n-1)}/2 + 1st term
=>(n)th term = 8*{n*(n-1)}/2 +2;
So, Clearly 87th term of the sequence will be :
8*{n*(n-1)}/2 +2 = 8*{87*86}/2 +2 = 4*86*87 +2 = 29930

Hence, 87th term will be : 29930

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rahul bhatiwal  (11 years ago)

its general term will be (2n-1)^2 + 1 ...put n= 87...so ans will be 299230

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DEEPU KUMAR  (11 years ago)

series is increasing as 2, 2+8*1 ,2+8*1+8*2 , 2+8*1+8*2+8*3,....up to n..
so 87 th term will be as
2+8*1+8*2+8*3+....+8*86
=2+8(1+2+3+4+...+86)
=2+8*(86*87/2)
=2+29928
=29930 ans.

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