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Arithmetic Progression - Quant/Math - CAT 2009
Question 4 the day:
October 03, 2003
The question for the day is from the topic of Arithmetic Progression.
- The sum of 20 terms of the series –12 + 22 – 32 + 42 – 52 + 62 … is:
| (1) |
210 |
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(2) |
519 |
| (3) |
190 |
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(4) |
None of these. |
Correct Answer - (1)
Solution:
–12 + 22 – 32 + 42 – 52 + 62 … upto 20 terms can be written as
(-12 + 22) + (–32 + 42) + (–52 + 62) + … upto 20 terms.
(-1 + 2) (1 + 2) + (-3 + 4) (3 + 4) + (-5 + 6) (5 + 6) +… (-19 + 20) (19 + 20)
(1 + 2) + (3 + 4) + (5 + 6) +… (19 + 20) = (20 * 21) / 2 = 210.
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