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The sequence Sn has the terms S1=1, S2=2, S3=6, S4=15, S5=31, ……. If
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25 Sep 2018, 02:42
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[ Math Revolution GMAT math practice question] The sequence S n has the terms S1=1, S 2=2, S 3=6, S 4=15, S 5=31, ……. If n is a positive integer, what could be the value of S nS n1 in terms of n? \(A. n\) \(B. n^2\) \(C. –n\) \(D. n^2\) \(E. (n1)^2\)
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Re: The sequence Sn has the terms S1=1, S2=2, S3=6, S4=15, S5=31, ……. If
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25 Sep 2018, 03:09
We see that the increment in the given sequence is: From S1 to S2: +1 = 1^2 From S2 to S3: +4 = 2^2 From S3 to S4: +9 = 3^2 From S4 to S5: +16 = 4^2 ... Thus from Sn1 to Sn = (n1)^2. Answer E
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Re: The sequence Sn has the terms S1=1, S2=2, S3=6, S4=15, S5=31, ……. If
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25 Sep 2018, 04:30
MathRevolution wrote: [ Math Revolution GMAT math practice question] The sequence S n has the terms S1=1, S 2=2, S 3=6, S 4=15, S 5=31, ……. If n is a positive integer, what could be the value of S nS n1 in terms of n? \(A. n\) \(B. n^2\) \(C. –n\) \(D. n^2\) \(E. (n1)^2\) To answer any question of sequences, one needs to find a pattern so we keep looking at what we get when we canculate expressions like \(S_n  S_{n1}\)\(S_1 = 1\) \(S_2 = 2\) i.e. \(S_2  S_{1} = 1= 1^1\) \(S_3 = 6\) i.e. \(S_3  S_{2} = 4 = 2^2\) \(S_4 = 15\) i.e. \(S_4  S_{3} = 9 = 3^2\) i.e. \(S_n  S_{n1} = (n1)^2\) Answer: Option E
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Re: The sequence Sn has the terms S1=1, S2=2, S3=6, S4=15, S5=31, ……. If
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25 Sep 2018, 08:57
MathRevolution wrote: [ Math Revolution GMAT math practice question] The sequence S n has the terms S1=1, S 2=2, S 3=6, S 4=15, S 5=31, ……. If n is a positive integer, what could be the value of S nS n1 in terms of n? \(A. n\) \(B. n^2\) \(C. –n\) \(D. n^2\) \(E. (n1)^2\) If you don't spot a pattern, you can always TEST the answer choicesWe want to find Sn  Sn1 So, let's test a value of n. How about n = 2So, we want to find the value of S 2  S1 Well, we're told that S 2 = 2 and S1 = 1 So, S 2  S1 = 2  1 = 1So, when n = 2, the answer to the question (what is the value of Sn  Sn1) is 1Now we'll check the answer choices to see which one yields an OUTPUT of 1 when we input n = 2A. n = 2. NO GOOD. We need an output of 1. ELIMINATE B. n² = 2² = 4. NO GOOD. We need an output of 1. ELIMINATE C. n =  2 = 2. NO GOOD. We need an output of 1. ELIMINATE D. n² =  2² = 4. NO GOOD. We need an output of 1. ELIMINATE E. (n  1)² = ( 2  1)² = 1. perfect!! Answer: E Cheers, Brent
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Re: The sequence Sn has the terms S1=1, S2=2, S3=6, S4=15, S5=31, ……. If
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26 Sep 2018, 23:56
=> We begin by writing out the terms of the sequence: S 2S 1 \(= 2 1 = 1=1^2\) S 3S 2 \(= 6 – 2 = 4 = 2^2\) S 4S 3 \(= 15 – 6 = 9 = 3^2\) S 5S 4 \(= 3115 = 16 = 4^2\) … Following the above pattern gives S nS n1 \(= (n1)^2\) Therefore, the answer is E. Answer: E
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Re: The sequence Sn has the terms S1=1, S2=2, S3=6, S4=15, S5=31, ……. If &nbs
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26 Sep 2018, 23:56






