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M19-28

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M19-28  [#permalink]

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New post 16 Sep 2014, 00:06
1
2
00:00
A
B
C
D
E

Difficulty:

  45% (medium)

Question Stats:

71% (01:25) correct 29% (01:50) wrong based on 184 sessions

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At 15:00 there were 20 students in the computer lab. At 15:03 and every three minutes after that, 3 students entered the lab. If at 15:10 and every ten minutes after that 8 students left the lab, how many students were in the computer lab at 15:44 ?

A. 7
B. 14
C. 25
D. 27
E. 30

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Re M19-28  [#permalink]

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New post 16 Sep 2014, 00:06
1
2
Official Solution:

At 15:00 there were 20 students in the computer lab. At 15:03 and every three minutes after that, 3 students entered the lab. If at 15:10 and every ten minutes after that 8 students left the lab, how many students were in the computer lab at 15:44 ?

A. 7
B. 14
C. 25
D. 27
E. 30

During the 44 minutes between 15:00 and 15:44 \(\frac{42}{3} = 14\) groups, 3 students each, entered the lab and \(\frac{40}{10} = 4\) groups, 8 students each, left the lab. Thus, the number of students in the lab grew by \(14*3 - 8*4 = 10\).

Answer: E
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New to the Math Forum?
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Resources:
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Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


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Re M19-28  [#permalink]

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New post 12 Aug 2017, 01:41
I think this is a high-quality question and I agree with explanation. in love with this question. AMAZING
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Re: M19-28  [#permalink]

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New post 08 Oct 2017, 22:20
This is a high quality question.

Posted from my mobile device
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Re: M19-28  [#permalink]

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New post 03 Sep 2018, 08:57
Bunuel wrote:
Official Solution:

At 15:00 there were 20 students in the computer lab. At 15:03 and every three minutes after that, 3 students entered the lab. If at 15:10 and every ten minutes after that 8 students left the lab, how many students were in the computer lab at 15:44 ?

A. 7
B. 14
C. 25
D. 27
E. 30

During the 44 minutes between 15:00 and 15:44 \(\frac{42}{3} = 14\) groups, 3 students each, entered the lab and \(\frac{40}{10} = 4\) groups, 8 students each, left the lab. Thus, the number of students in the lab grew by \(14*3 - 8*4 = 10\).

Answer: E



Can someone please explain this in detail. How did we get 42 and 40 in numerators.
Math Expert
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Joined: 02 Sep 2009
Posts: 51185
Re: M19-28  [#permalink]

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New post 03 Sep 2018, 22:47
mischiefmanaged wrote:
Bunuel wrote:
Official Solution:

At 15:00 there were 20 students in the computer lab. At 15:03 and every three minutes after that, 3 students entered the lab. If at 15:10 and every ten minutes after that 8 students left the lab, how many students were in the computer lab at 15:44 ?

A. 7
B. 14
C. 25
D. 27
E. 30

During the 44 minutes between 15:00 and 15:44 \(\frac{42}{3} = 14\) groups, 3 students each, entered the lab and \(\frac{40}{10} = 4\) groups, 8 students each, left the lab. Thus, the number of students in the lab grew by \(14*3 - 8*4 = 10\).

Answer: E



Can someone please explain this in detail. How did we get 42 and 40 in numerators.


First 3 students entered the lab at 15:03. Next:
15:06;
15:12;
...
15:39
Last 3 students entered the lab at 15:42.

As you can see we have multiples of 3 from 3 to 42 inclusive. How many multiples of 3 are there in this range? (42 - 3)/3 + 1 = 14.

First 8 student group left the lat at 15:10.
15:20
15:30
15:40.
4 groups, 8 students each, left the lab.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

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Posts: 8
Re: M19-28  [#permalink]

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New post 04 Sep 2018, 00:27
Bunuel wrote:
mischiefmanaged wrote:
Bunuel wrote:
Official Solution:

At 15:00 there were 20 students in the computer lab. At 15:03 and every three minutes after that, 3 students entered the lab. If at 15:10 and every ten minutes after that 8 students left the lab, how many students were in the computer lab at 15:44 ?

A. 7
B. 14
C. 25
D. 27
E. 30

During the 44 minutes between 15:00 and 15:44 \(\frac{42}{3} = 14\) groups, 3 students each, entered the lab and \(\frac{40}{10} = 4\) groups, 8 students each, left the lab. Thus, the number of students in the lab grew by \(14*3 - 8*4 = 10\).

Answer: E



Can someone please explain this in detail. How did we get 42 and 40 in numerators.


First 3 students entered the lab at 15:03. Next:
15:06;
15:12;
...
15:39
Last 3 students entered the lab at 15:42.

As you can see we have multiples of 3 from 3 to 42 inclusive. How many multiples of 3 are there in this range? (42 - 3)/3 + 1 = 14.

First 8 student group left the lat at 15:10.
15:20
15:30
15:40.
4 groups, 8 students each, left the lab.


Thank you very much.
GMAT Club Bot
Re: M19-28 &nbs [#permalink] 04 Sep 2018, 00:27
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