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03 Oct 2019, 23:59
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B
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
55%
(hard)
Question Stats:
61% (01:49) correct
39%
(01:49)
wrong
based on 200
sessions
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Not Attempted Yet
What is the sum of the following series? -64, -66, -68, ..... , -100
A-1458
B-1558
C-1568
D-1664
E None of the above
A-1458
B-1558
C-1568
D-1664
E None of the above
04 Oct 2019, 03:14
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The consecutive numbers in the series differ by -2 (i.e -66 - (-64) = -2), so it is an Arithmetic Series
Last term is given as -100 and first terms is -64 and common difference = -2
So, to find sum of all the terms we need to find the total number of terms first.
In an arithmetic series number of terms,n, is given by (Last term - First Term)/common difference + 1
so, n = (-100 - (-64))/-2 + 1 = 18 + 1 = 19
Sum of n terms of Arithmetic series is given by, s = number of terms * mean of first and last term = 19* (-64 + -100)/2 = 19 * -82 = -1558
So, Answer is B
Hope it helps.
P.S.: I have also attached the formulas for Arithmetic Series (Arithmetic progression) with this post for your reference.
Last term is given as -100 and first terms is -64 and common difference = -2
So, to find sum of all the terms we need to find the total number of terms first.
In an arithmetic series number of terms,n, is given by (Last term - First Term)/common difference + 1
so, n = (-100 - (-64))/-2 + 1 = 18 + 1 = 19
Sum of n terms of Arithmetic series is given by, s = number of terms * mean of first and last term = 19* (-64 + -100)/2 = 19 * -82 = -1558
So, Answer is B
Hope it helps.
P.S.: I have also attached the formulas for Arithmetic Series (Arithmetic progression) with this post for your reference.
Attachments
File comment: Formulas for AP
AP.jpg [ 203.02 KiB | Viewed 5189 times ]
05 Aug 2022, 07:57
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dharam44
Note: The GMAT doesn't test our ability to find missing terms in a sequence (or determine the patter) unless the sequence is specifically defined for us. The reason is that there's no way that we can definitively determine ONE (and ONLY ONE) pattern in a given sequence.
Consider this official GMAT question: https://gmatclub.com/forum/what-is-the- ... 24942.html
Here, we’re told the first five terms of sequence S are 1^2, 2^2, 3^2, 4^2, and 5^2, but that still isn’t sufficient information to determine the 1000th term.
Cheers,
Brent
