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# If a_n = a_1 + (n - 1)d, what is the value of a_51?

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Math Expert
Joined: 02 Sep 2009
Posts: 58473
If a_n = a_1 + (n - 1)d, what is the value of a_51?  [#permalink]

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03 Apr 2018, 21:27
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Difficulty:

25% (medium)

Question Stats:

76% (01:12) correct 24% (00:50) wrong based on 56 sessions

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If $$a_n = a_1 + (n - 1)d$$, what is the value of $$a_{51}$$?

(1) $$a_{11} = 25$$

(2) $$a_{21} = 45$$

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Math Expert
Joined: 02 Sep 2009
Posts: 58473
Re: If a_n = a_1 + (n - 1)d, what is the value of a_51?  [#permalink]

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03 Apr 2018, 21:28
Bunuel wrote:
If $$a_n = a_1 + (n - 1)d$$, what is the value of $$a_{51}$$?

(1) $$a_{11} = 25$$

(2) $$a_{21} = 45$$

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Joined: 05 Feb 2016
Posts: 167
Location: India
Concentration: General Management, Marketing
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Re: If a_n = a_1 + (n - 1)d, what is the value of a_51?  [#permalink]

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03 Apr 2018, 21:58
Bunuel wrote:
If $$a_n = a_1 + (n - 1)d$$, what is the value of $$a_{51}$$?

(1) $$a_{11} = 25$$

(2) $$a_{21} = 45$$

from1 :
$$a_{11} = 25$$
then
$${11} = a_1 + (11 - 1)d$$,
two variables a_1 and d
one equation ,so insufficent.

from2: two variables a_1 and d
one equation ,so insufficent.

combinig both: two variables two equation hence sufficient.

C
Re: If a_n = a_1 + (n - 1)d, what is the value of a_51?   [#permalink] 03 Apr 2018, 21:58
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