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# A local restaurant draws a business card from a jar every day. The per

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Math Expert
Joined: 02 Sep 2009
Posts: 61510
A local restaurant draws a business card from a jar every day. The per  [#permalink]

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04 Dec 2019, 01:44
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Difficulty:

45% (medium)

Question Stats:

54% (01:29) correct 46% (01:39) wrong based on 52 sessions

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A local restaurant draws a business card from a jar every day. The person whose name is drawn receives a free meal. Floyd drops his business card in the jar at the beginning of the month. Thirty days later, assuming that his card hasn't been drawn yet, what is the percent change in the probability that Floyd's card will be drawn from the jar on the next drawing?

(1) Only one card is drawn from the jar every day.

(2) On average, 10 business cards are added to the jar everyday.

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Re: A local restaurant draws a business card from a jar every day. The per  [#permalink]

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04 Dec 2019, 19:35
Bunuel wrote:
A local restaurant draws a business card from a jar every day. The person whose name is drawn receives a free meal. Floyd drops his business card in the jar at the beginning of the month. Thirty days later, assuming that his card hasn't been drawn yet, what is the percent change in the probability that Floyd's card will be drawn from the jar on the next drawing?

(1) Only one card is drawn from the jar every day.

(2) On average, 10 business cards are added to the jar everyday.

Are You Up For the Challenge: 700 Level Questions

Percentage change requires number before and after.

Statement I just repeats the info that is already given in the question stem.
Statement II tells us that 10 are added on an average.

But we still do not know what is the actual number.
Change in the month - 10 added every day and 1 subtracted, so net change 9 added. In a month 9*30=270 added.
Say we started with 30 business cards, so in end of the month there are 300 cards....probability =1/300

We cannot determine the probability or % change

E
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Re: A local restaurant draws a business card from a jar every day. The per  [#permalink]

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05 Dec 2019, 05:54
Bunuel wrote:
A local restaurant draws a business card from a jar every day. The person whose name is drawn receives a free meal. Floyd drops his business card in the jar at the beginning of the month. Thirty days later, assuming that his card hasn't been drawn yet, what is the percent change in the probability that Floyd's card will be drawn from the jar on the next drawing?

(1) Only one card is drawn from the jar every day.

(2) On average, 10 business cards are added to the jar everyday.

Are You Up For the Challenge: 700 Level Questions

We are missing the number of cards in the jar since Floyd dropped his card in.
If there were 10 cards at the beginning of the month, the probability, in the beginning, is 1/10 and 30 days later the probability is 1/310. As we can see the percent change is quite big.
If there were 10000 cards at the beginning of the month, the probability, in the beginning, is 1/10000 can 30 days later the probability is 1/10300. The percent change is negligible.

Ans: E
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Re: A local restaurant draws a business card from a jar every day. The per   [#permalink] 05 Dec 2019, 05:54
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