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# If from 1991 to 2000, the number of students of School X tripled, how

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Math Expert
Joined: 02 Sep 2009
Posts: 58445
If from 1991 to 2000, the number of students of School X tripled, how  [#permalink]

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29 Oct 2018, 04:56
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Difficulty:

25% (medium)

Question Stats:

86% (01:10) correct 14% (00:40) wrong based on 44 sessions

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If from 1991 to 2000, the number of students of School X tripled, how many number of students of the school were there in 1991?

(1) From 2000 to 2009, the number of students of the school doubled.
(2) From 2000 to 2009, the number of students of the school increased by 120.

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Re: If from 1991 to 2000, the number of students of School X tripled, how  [#permalink]

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29 Oct 2018, 05:26
1
Let the number of students in School X be S.
Given that from 1991 to 2000. Students tripled. So in 2000, the number of students became 3S.

From statement 1:

From 2000 to 2009. Students doubled. Then 3S becomes 6S.
Still S is unknown.
Insufficient.

From statement 2:

From 2000 to 2009. Students increased by 120. But no info about Percentage of increase or by how many times the students increased.
Insufficient.

Combining both.

Students doubled from 3S to 6S. Also 6S-3S = 120.
S = 40. The number of students in 1990 was 40.
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Re: If from 1991 to 2000, the number of students of School X tripled, how  [#permalink]

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01 Nov 2018, 23:55
If from 1991 to 2000, the number of students of School X tripled, how many number of students of the school were there in 1991?

(1) From 2000 to 2009, the number of students of the school doubled.
(2) From 2000 to 2009, the number of students of the school increased by 120.

We know
1991 - X
2000 - 3X

1. 2009 - 6X. Not sufficient.
2. 3X + 120. Not sufficient.

Together,
6X = 3X + 120
Sufficient.
C.
Re: If from 1991 to 2000, the number of students of School X tripled, how   [#permalink] 01 Nov 2018, 23:55
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