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Bert and Clair's coins (OG13)

This topic has 2 expert replies and 2 member replies
alex.gellatly Master | Next Rank: 500 Posts Default Avatar
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Bert and Clair's coins (OG13)

Post Thu Aug 02, 2012 10:02 pm
What is the total number of coins that Bert and Claire have?
(1) Bert has 50 percent more coins than Claire.
(2) The total number of coins that Bert and Claire have is between 21 and 28.

OK, I got the correct answer by picking numbers and kind of guessing. Can someone show me a good algebraic approach?

Thanks!

_________________
A useful website I found that has every quant OG video explanation:

http://www.beatthegmat.com/useful-website-with-og-video-explanations-t112985.html#475231

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vinodsundaram Senior | Next Rank: 100 Posts Default Avatar
Joined
21 May 2012
Posted:
58 messages
Upvotes:
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Test Date:
08/16/2012
Target GMAT Score:
720
Top Reply
Post Mon Aug 06, 2012 1:36 am
there's catch in these kind of problems.

Once you combine both equations, you solve and get multiple answers.
It is important to ELIMINATE All possible wrong answers.

We know Coins can always be Positive numbers. Hence using the relation between B and C we can eliminate.

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Post Fri Aug 03, 2012 10:09 am
alex.gellatly wrote:
What is the total number of coins that Bert and Claire have?
(1) Bert has 50 percent more coins than Claire.
(2) The total number of coins that Bert and Claire have is between 21 and 28.

OK, I got the correct answer by picking numbers and kind of guessing. Can someone show me a good algebraic approach?

Thanks!
This problem is restricted to POSITIVE INTEGERS.

Statement 1: Bert has 50 percent more coins than Claire.
Thus, if C=2, then B = (1.5)2 = 3, implying that B:C = 3:2.
Since the sum of the parts of this ratio = 3+2 = 5, the total number of coins must be a multiple of 5.
INSUFFICIENT.

Statement 2: The total number of coins that Bert and Claire have is between 21 and 28.
Thus, the total number of coins could be any integer between 21 and 28.
INSUFFICIENT.

Statements 1 and 2 combined:
The only multiple of 5 between 21 and 28 is 25.
SUFFICIENT.

The correct answer is C.

_________________
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vinodsundaram Senior | Next Rank: 100 Posts Default Avatar
Joined
21 May 2012
Posted:
58 messages
Upvotes:
1
Test Date:
08/16/2012
Target GMAT Score:
720
Post Mon Aug 06, 2012 1:36 am
there's catch in these kind of problems.

Once you combine both equations, you solve and get multiple answers.
It is important to ELIMINATE All possible wrong answers.

We know Coins can always be Positive numbers. Hence using the relation between B and C we can eliminate.

  • +1 Upvote Post
  • Quote
  • Flag
Post Fri Aug 03, 2012 10:09 am
alex.gellatly wrote:
What is the total number of coins that Bert and Claire have?
(1) Bert has 50 percent more coins than Claire.
(2) The total number of coins that Bert and Claire have is between 21 and 28.

OK, I got the correct answer by picking numbers and kind of guessing. Can someone show me a good algebraic approach?

Thanks!
This problem is restricted to POSITIVE INTEGERS.

Statement 1: Bert has 50 percent more coins than Claire.
Thus, if C=2, then B = (1.5)2 = 3, implying that B:C = 3:2.
Since the sum of the parts of this ratio = 3+2 = 5, the total number of coins must be a multiple of 5.
INSUFFICIENT.

Statement 2: The total number of coins that Bert and Claire have is between 21 and 28.
Thus, the total number of coins could be any integer between 21 and 28.
INSUFFICIENT.

Statements 1 and 2 combined:
The only multiple of 5 between 21 and 28 is 25.
SUFFICIENT.

The correct answer is C.

_________________
Mitch Hunt
GMAT Private Tutor
GMATGuruNY@gmail.com
If you find one of my posts helpful, please take a moment to click on the "Thank" icon.
Available for tutoring in NYC and long-distance.
For more information, please email me at GMATGuruNY@gmail.com.

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  • Flag
Free GMAT Practice Test How can you improve your test score if you don't know your baseline score? Take a free online practice exam. Get started on achieving your dream score today! Sign up now.

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