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(#M40115073) TCS Numerical Ability question series Keep an EYE

87th number in the series 2, 10, 26,
50,……….

Asked In TCS shikha (10 years ago)

Solved kshitij gupta Read Solution (11)

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kshitij gupta  (10 years ago) Best Solution

2+8*0=2
2+8*1=10
2+8*1+8*2=26
2+8*1+8*2+8*3=50...........
87th term
2+8*1+8*2+8*3+.......................................+8*86
2+8(1+2+3+4+....................+86)
2+8*(86/2)*(1+86)= 29930

Is this solution Helpfull? Yes (70) | No (2)  

shikha  (10 years ago)

how can we take d=8. ? its not an AP

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

Rijomon Jose  (10 years ago)

here we can use formula : an=a+(n-1)*d
a=2
n=87
d=8
an=2+86*8
an=690

Is this solution Helpfull? Yes (3) | No (32)  

Sitanshu  (10 years ago)

2
2+8
2+8+8*2
2+8+8*2+8*3
87th term= 2+ 8*(1+2+3+.....86)=2+8*86/2*87=2+4*86*87=29930

Is this solution Helpfull? Yes (3) | No (1)  

N LOHITHKUMAR  (10 years ago)

1^2+1,3^2+1,5^2+1................
A+(N-1)D=1+(87-1)*2=29929
29929+1=29930

Is this solution Helpfull? Yes (3) | No (2)  

ALEX P T  (10 years ago)

diff b/w 2 and 10 is 8
diff b/w 10 and 26 is 16
diff b/w 26 and 50 is 24
so diff series is 8, 16 , 24,and so on series continues..... so find 86th term in this series i.e.29928 and add 2 to that, then we will get actual 87th term in the required series that is 29930.

Is this solution Helpfull? Yes (2) | No   

Nidadavolu.Suneetha  (10 years ago)

87th no. is 700.
2nd term=1st term+8
3rd term=1st term+2(8)
.
.
87th term=1st term+86(8)
=2+688=700

Is this solution Helpfull? Yes (2) | No (3)  

prabhat kumar  (10 years ago)

mandira your answer is correct...kshitij and sitanshu u both are finding the sum upto 87th no..we just have to find 87th no..
if we subtract second no by first we get an secondary AP..
8,16,24...

now take a=8 n=86 d=8

t87=8+(86-1)*8
t87=688

Is this solution Helpfull? Yes (1) | No (11)  

mandira  (10 years ago)

since 87th number is required:
86*8= 688

Is this solution Helpfull? Yes | No (5)  

Manideepa Rana  (10 years ago)

And is 82
10-2=8 =8*1
26-10=16=8*2
50-26=24=8*3
So the next no. will be 50+(8*4)=50+32=82

Is this solution Helpfull? Yes | No (6)  

arpit jain  (9 years ago)

As the difference among the terms is constant.....apply Tn=an^2+bn+c.

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