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# If S = n(n + 1)/2 and n = 40, then S =

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Math Expert
Joined: 02 Sep 2009
Posts: 59182
If S = n(n + 1)/2 and n = 40, then S =  [#permalink]

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15 Oct 2019, 07:02
00:00

Difficulty:

15% (low)

Question Stats:

100% (00:32) correct 0% (00:00) wrong based on 20 sessions

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If $$S = \frac{n(n + 1)}{2}$$ and $$n = 40$$, then $$S =$$

A. 121
B. 162
C. 420
D. 780
E. 820

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Joined: 15 Aug 2017
Posts: 24
Re: If S = n(n + 1)/2 and n = 40, then S =  [#permalink]

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15 Oct 2019, 07:36
Bunuel wrote:
If $$S = \frac{n(n + 1)}{2}$$ and $$n = 40$$, then $$S =$$

A. 121
B. 162
C. 420
D. 780
E. 820

$$S = \frac{40(40 + 1)}{2}$$
$$S = \frac{40^2 + 40}{2}$$
$$S = \frac{1600 + 40}{2}$$
$$S = \frac{1640}{2}$$

S = 820
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Re: If S = n(n + 1)/2 and n = 40, then S =  [#permalink]

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15 Oct 2019, 07:45
Bunuel wrote:
If $$S = \frac{n(n + 1)}{2}$$ and $$n = 40$$, then $$S =$$

A. 121
B. 162
C. 420
D. 780
E. 820

$$S = \frac{40*41}{2}$$

Or, $$S = 20*41$$

Or, $$S = 820$$ , Answer must be (E)
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Re: If S = n(n + 1)/2 and n = 40, then S =  [#permalink]

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15 Oct 2019, 11:56
20*41= 820. Hence E
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Re: If S = n(n + 1)/2 and n = 40, then S =   [#permalink] 15 Oct 2019, 11:56
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