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(#M40154001) TCS Logical Reasoning question SERIES Keep an EYE

What is 87th term in series:
2.10.26.50?

ans-3741

Asked In TCS TAUSEEF AMEEN (9 years ago)

Unsolved Read Solution (5)

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Read Solution (5) :

KHUSHBOO  (9 years ago)

2=1^2+1
10=3^2+1
26=5^2+1
..........
here ,1,3,5,7...... are odd numbers so by using An=a+(n-1)d
we can find the A87 th term for odd no. series..
A87=1+(87-1)x 2= 173
so ,the 87th term will be...
173^2+1=29930

ans: 29930

Is this solution Helpfull? Yes (20) | No (3)  

ANKIT PATEL  (9 years ago)

as per the given series
Tn=T(n-1) +8*(n-1)
T87= T86+ 8*86
T87=2+8*(1+2+3............86)
T87= 2+8*(86*87/2)
T87=2+3741
T87=3743

Is this solution Helpfull? Yes (7) | No (5)  

Shiv R Yadav  (6 years ago)

Consider the AP 0,8,16,24,,...........87th term is 688
a = 0
d=8
t87 = 87/2 ( 2(0)+(86)8) = 29928
as series starts from 2
add 2
answer is 29928 + 2 = 29930

Is this solution Helpfull? Yes (2) | No   

Shubham gupta  (8 years ago)

ans is 2066

Is this solution Helpfull? Yes | No (1)  

Vattikonda Shainy  (6 years ago)

-->The difference b/w each num= Multiples of 8.
The nth term of the main series can be expressed as :

2 + sum of the series 8, 16, 32… till (n-1) terms

2 = 2+0
10 = 2+ 8
26 = 2 + 24 = 2 + (8 +16)
50 = 2 + 48 = 2 + (8 + 16 + 24)
.
..
nth term = 2 + (8+16+24+ ...+ till (n-1))
Therefore, the sum of 8, 16, 32… till (n-1) using the formula for the sum of an arithmetic progression will be

S=n−12[16+(n−2)8]

This simplifies as,

4n(n−1)
Thus the general term of the main series will be,

Tn=2+4n(n−1)

.

.

Thus the 87th term is

T87=2+4×87×86

T87=29930

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