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15 May 2019, 02:01
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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:
75%
(hard)
Question Stats:
57% (02:08) correct
43%
(02:25)
wrong
based on 508
sessions
History
Date
Time
Result
Not Attempted Yet
A certain series of numbers has 15 terms in total. The first term of the sequence is -4. From the second term, every even numbered term is 3 more than the previous term, and every odd numbered term is 2 less than the previous term. How many terms are positive in the given series?
- A. 7
B. 8
C. 9
D. 10
E. 11
Archit3110
Major Poster
15 May 2019, 10:12
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Based on my understanding of the question ; solution as follows;
a1=-4
a2=-4+3;-1
a3=-1-2;-3
continue with same logic until a15
a4;0
a5;-2
a6;1
a7;-1
a8;2
a9;0
a10;3
a11;1
a12;4
a13;2
a14;5
a15;3
not to count 0 ; we get get 8 +ve integers
IMO B
a1=-4
a2=-4+3;-1
a3=-1-2;-3
continue with same logic until a15
a4;0
a5;-2
a6;1
a7;-1
a8;2
a9;0
a10;3
a11;1
a12;4
a13;2
a14;5
a15;3
not to count 0 ; we get get 8 +ve integers
IMO B
EgmatQuantExpert
20 May 2019, 04:03
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Solution
Given:
In this question, we are given that
- • A certain series of numbers has 15 terms in total.
• The first term of the sequence is -4.
• From the second term, every even numbered term is 3 more than the previous term, and every odd numbered term is 2 less than the previous term.
To find:
We need to determine
- • The number of terms in the series, which are positive.
Approach and Working:
Let us determine the values of the individual terms, using the value of the first term.
- • Term 1 = -4
• Term 2 = -4 + 3 = -1
• Term 3 = -1 – 2 = -3
• Term 4 = -3 + 3 = 0
• Term 5 = 0 – 2 = -2
• Term 6 = -2 + 3 = 1
• Term 7 = 1 – 2 = -1
• Term 8 = -1 + 3 = 2
• Term 9 = 2 – 2 = 0
• Term 10 = 0 + 3 = 3
Term 10 onwards all the terms will be positive.
As we can see, there are total 7 terms present in the series, which are either negative or 0.
- • Therefore, the number of positive terms = 15 – 7 = 8
Hence, the correct answer is option B.
Answer: B
