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Numerical Ability
Sequence and Series
Consider the sequence 1,-2, 3,-4, 5,-6, ….. , what is the average of the first 2000 terms of the sequence?
Read Solution (Total 15)
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- Ans is -1/2
=-(1+1+1.....upto 1000 trms)/2000
=-1/2 - 10 years agoHelpfull: Yes(21) No(1)
- (1,3,5,..1999) here n=1000
s1=n/2(2a+(n-1)d)=10000000
(-2,-4,-6...,-2000) here n=1000
s2=-1001000
so avg term= s1+s2/2000term
=-1000/2000
=-1/2 ans.
- 10 years agoHelpfull: Yes(4) No(0)
- ans.=-1/2
-1-1-1....(1000th)/2000 - 10 years agoHelpfull: Yes(2) No(0)
- 1-2=-1
3-4=-1
.
.
.
.
-1,1000 times
so ans=-1000/2000
=-1/2 - 10 years agoHelpfull: Yes(2) No(0)
- @KARTHIKEYAN
TOTAL 2000 TERMS
JUST TAKE IT THE PAIR SEQUENCE EX:(1,-2)
SO 1000 PAIRS IN 2000 TERMS
- 10 years agoHelpfull: Yes(2) No(1)
- ans is -1/2..
- 10 years agoHelpfull: Yes(2) No(0)
- Ans is -1/2
=-(1+1+1.....upto 100 trms)/200
=-1/2 - 10 years agoHelpfull: Yes(1) No(0)
- 1+3+5...1000 terms + -2-4-6..1000 terms
1000/2[(2+(999*2))+2*(999*-2)]
=-998000 - 10 years agoHelpfull: Yes(0) No(6)
- pls explain in the ans karthi
- 10 years agoHelpfull: Yes(0) No(0)
- ( on comininig 2 term eg((1,-2)(3,-4)...) we get -1 for 2000 term sum would be
-1000) av =(-1000)/2000
=-1/2 - 10 years agoHelpfull: Yes(0) No(0)
- first sequence is 1,3,5...... (1000 terms )
second sequence is -2,-4.-6........ (1000 terms)
use formula to find the sum of series =(n/2)(2a+(n-1)d)
answere = -1/2 - 10 years agoHelpfull: Yes(0) No(0)
- @Karthikeyank:
(-1/2) is incorrect.
Average of a series is always positive.
ans is (+1/2) - 10 years agoHelpfull: Yes(0) No(1)
- sum=500*(2+4)+500*(-4-4)/2000=-.5
- 10 years agoHelpfull: Yes(0) No(0)
- ans is -0.5
- 9 years agoHelpfull: Yes(0) No(0)
- see guyzz, here 1,-2,3,-4,.....,200
now if we know that what is the answer of first 10 terms then we can calculate the for 200 terms.
here summing first 10 terms
1-2+3-4+5-6+7-8+9-10
=-1-1-1-1-1
=-5
here for 10 terms answer is half 10/2=-5
so that for 200=200/2=-100
and for average total by total numbers=-100/200=-.5 - 9 years agoHelpfull: Yes(0) No(0)
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