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Mark is playing poker at a casino. Mark starts playing with

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Mark is playing poker at a casino. Mark starts playing with [#permalink] New post 11 Nov 2004, 03:59
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64% (04:57) correct 36% (04:18) wrong based on 66 sessions
Mark is playing poker at a casino. Mark starts playing with 140 chips, 20% of which are $100 chips and 80% of which are $20 chips. For his first bet, Mark places chips, 10% of which are $100 chips, in the center of the table. If 70% of Mark's remaining chips are $20 chips, how much money did Mark bet?

A. $1,960
B. $1,740
C. $1,540
D. $3,080
E. $2,640
[Reveal] Spoiler: OA

Last edited by Bunuel on 17 Nov 2014, 11:26, edited 1 time in total.
Added the OA.
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Re: Mark is playing poker at a casino. Mark starts playing with [#permalink] New post 11 Nov 2004, 06:23
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A. 1960.

Let's say he bet X $100 chips, which means 9X $20 chips.
Out of the 140 chips, 112 are $20 chips and 28 are $100 chips.

0.7*(140-10X) = 112-9X.

You get X=7.

7*100 + 9*7*20 = 1960.
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Re: Mark is playing poker at a casino. Mark starts playing with [#permalink] New post 17 Nov 2014, 11:22
bump for a good practice question :)

If Mark has 140 chips and 20% are $100 chips, then Mark has 1/5 of 140 or 28 $100 chips. The other 112 are $20 chips.

10% of the chips he bet were $100 chips so for every 10 chips he bet, the total must have been $100 + 9($20) = $280. We can divide each answer choice by this # to see which one works.

A. 1960/280 = 7, meaning that Frank bet 7 $100 chips and 63 $20 chips. This would bring his total chip count to 140-7-63=70 chips and his $20 chip count down to 112-63=59 chips. So he has 59/70 $20 chips remaining. 70% is what we are looking for which is slighly less than 3/4 and this fraction is much more than that so we need a bigger answer.

B. we need a # larger than answer A so this wont work
C. same reason as above
D. 3080 / 280 = 11 meaning Frank bet 11 $100 chips and 99 $20 chips. He now has 30 chips left, 13 of which are $20 chips. 13/20 = 65/100 = 65% this is too small so we know Frank must have bet less money.

Answer E!
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Mark is playing poker at a casino. Mark starts playing with [#permalink] New post 17 Nov 2014, 22:47
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christoph wrote:
Mark is playing poker at a casino. Mark starts playing with 140 chips, 20% of which are $100 chips and 80% of which are $20 chips. For his first bet, Mark places chips, 10% of which are $100 chips, in the center of the table. If 70% of Mark's remaining chips are $20 chips, how much money did Mark bet?

A. $1,960
B. $1,740
C. $1,540
D. $3,080
E. $2,640


Initially, he had 80% $20 chips. Then he bet an amount in which he had 90% $20 chips and was left with an amount in which there were 70% $20 chips. Since 80% is the mid of 70% and 90%, it means the number of chips in the two cases were equal. So he bet a total of 140/2 = 70 chips.

7 must be $100 chips with value $700
63 must be $20 chips with value 63*20 = $1260
Total value of the bet = $1960

Answer (A)
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Re: Mark is playing poker at a casino. Mark starts playing with [#permalink] New post 18 Nov 2014, 00:37
VeritasPrepKarishma wrote:
christoph wrote:
Mark is playing poker at a casino. Mark starts playing with 140 chips, 20% of which are $100 chips and 80% of which are $20 chips. For his first bet, Mark places chips, 10% of which are $100 chips, in the center of the table. If 70% of Mark's remaining chips are $20 chips, how much money did Mark bet?

A. $1,960
B. $1,740
C. $1,540
D. $3,080
E. $2,640


Initially, he had 80% $20 chips. Then he bet an amount in which he had 90% $20 chips and was left with an amount in which there were 70% $20 chips. Since 80% is the mid of 70% and 90%, it means the number of chips in the two cases were equal. So he bet a total of 140/2 = 70 chips.

7 must be $100 chips with value $700
63 must be $20 chips with value 63*20 = $1260
Total value of the bet = $1960

Answer (A)


Karishma, I love your weighted method but for this one, i was confused to figure out the reasoning behind it. So sorry but can you elaborate further? Thank you.
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Re: Mark is playing poker at a casino. Mark starts playing with [#permalink] New post 18 Nov 2014, 19:48
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vietnammba wrote:
VeritasPrepKarishma wrote:
christoph wrote:
Mark is playing poker at a casino. Mark starts playing with 140 chips, 20% of which are $100 chips and 80% of which are $20 chips. For his first bet, Mark places chips, 10% of which are $100 chips, in the center of the table. If 70% of Mark's remaining chips are $20 chips, how much money did Mark bet?

A. $1,960
B. $1,740
C. $1,540
D. $3,080
E. $2,640


Initially, he had 80% $20 chips. Then he bet an amount in which he had 90% $20 chips and was left with an amount in which there were 70% $20 chips. Since 80% is the mid of 70% and 90%, it means the number of chips in the two cases were equal. So he bet a total of 140/2 = 70 chips.

7 must be $100 chips with value $700
63 must be $20 chips with value 63*20 = $1260
Total value of the bet = $1960

Answer (A)


Karishma, I love your weighted method but for this one, i was confused to figure out the reasoning behind it. So sorry but can you elaborate further? Thank you.


Look, that's the thing about weighted averages - don't think of them only after you see terms such as average, mixture etc. They are useful whenever you talk about two groups separately and then together or about one group splitting into two groups.

Here, he has a bunch of 140 chips first with a concentration of 80% $20 chips. He splits the bunch into two groups:
One he bets with a concentration of 90% $20 chips
The other he keeps with a concentration of 70% $20 chips

The mix is the initial bunch. The 70% group combined with 90% group gives the 80% initial bunch of chips.
Now using the usual formula, w1/w2 = (90 - 80)/(80 - 70) = 1:1

The two groups will have equal chips.

Does the use of weighted avgs make sense now?
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Re: Mark is playing poker at a casino. Mark starts playing with [#permalink] New post 19 Nov 2014, 03:57
Karishma,

Thanks for sharing your knowledge. Could you please do the same with the 100 $ chips?

Thanks in advance

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Re: Mark is playing poker at a casino. Mark starts playing with [#permalink] New post 19 Nov 2014, 08:15
Great explaination as usual Karishma, thank you so much :)
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Re: Mark is playing poker at a casino. Mark starts playing with [#permalink] New post 19 Nov 2014, 19:37
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spla626 wrote:
Karishma,

Thanks for sharing your knowledge. Could you please do the same with the 100 $ chips?

Thanks in advance

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Yes, you can do the same with the other "ingredient" as well.

The mix has 20% $100 chips, he bet a bunch that has 10% $100 chips and was left with the other bunch that has 30% $100 chips.
w1/w2 = (30 - 20)/(20 - 10) = 1:1

Both bunches are equal.
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Re: Mark is playing poker at a casino. Mark starts playing with   [#permalink] 19 Nov 2014, 19:37
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