Any term in the sequence (except for the first and last terms) is the

Question

Any term in the sequence (except for the first and last terms) is the average of the two adjacent terms in the sequence . What is the 8th term in the sequence?

(1) First term is 2.

(2) Third term is 6.

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Edoua · Answer

We don’t know how many term the sequence has.

8th term can be (6+7 )/2 if number of term are more than 8 
If number of terms =8 we can not sum up those terms

Hence 1+2 insufficient

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BongBideshini · Answer

Mathematically, a_n = (a_{n-1} + a_{n+1})/2 
 i.e, a_{n+1} - a_n = a_n - a_{n-1}

This is the definition of an  Arithmetic Progression (AP).

Statement (1): First term is 2

We know a1 = 2, but we don't know the difference (d).  
   Insufficient.    
 Statement (2): Third term is 6

We know a3 = 6, but we don't know where the sequence started.   
   Insufficient.    
 Combined (1) and (2)

We have a1 = 2 and a3 = 6. 
We get d=2 
  We can now calculate the 8th term: 2 + (7 * 2) = 16  
   Sufficient.    
  Correct Answer: C

SantosT · Answer

Since we don ́t know if the 8th is the last term or not, we can ́t affirm that s1 + s2 is enough by applying the formula until 8th term.

Any term in the sequence (except for the first and last terms) is the

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GMAT Data Sufficiency (DS) Questions

Any term in the sequence (except for the first and last terms) is the

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