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# M09-35

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Math Expert
Joined: 02 Sep 2009
Posts: 52294

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15 Sep 2014, 23:41
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1
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Difficulty:

(N/A)

Question Stats:

78% (00:27) correct 22% (00:51) wrong based on 88 sessions

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If the probability that the typist will make a mistake on a page is $$\frac{1}{100}$$, what is the probability that the typist will type 100 pages without making a single mistake?

A. $$(\frac{1}{100})^{100}$$
B. $$\frac{1}{10}$$
C. $$(\frac{99}{100})^{100}$$
D. $$\frac{99}{100}$$
E. 1

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Math Expert
Joined: 02 Sep 2009
Posts: 52294

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15 Sep 2014, 23:41
1
Official Solution:

If the probability that the typist will make a mistake on a page is $$\frac{1}{100}$$, what is the probability that the typist will type 100 pages without making a single mistake?

A. $$(\frac{1}{100})^{100}$$
B. $$\frac{1}{10}$$
C. $$(\frac{99}{100})^{100}$$
D. $$\frac{99}{100}$$
E. 1

The probability that the typist will not make a mistake on a page is $$1 - \frac{1}{100} = \frac{99}{100}$$. The probability that she will not make a mistake in 100 pages is $$(\frac{99}{100})^{100}$$

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Joined: 10 May 2017
Posts: 27

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30 Jun 2017, 22:04
I agree with the explanation though i got it wrong. Read the question wrongly.

The probability of not making a mistake is (1-0.001) / page.

If the she types 100 pages then,

1st page no mistake = 99/100 "AND"
2nd page no mistake = 99/100 "AND"
.
.
.
.
100th page no mistake = 99/100.

When it is "AND", we multiply and therefore (99/100)^100.
Intern
Joined: 19 Jun 2017
Posts: 4

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31 May 2018, 17:31
How can a probability be more than 1??
here we get 99 :O
Math Expert
Joined: 02 Sep 2009
Posts: 52294

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31 May 2018, 22:15
Richin wrote:
How can a probability be more than 1??
here we get 99 :O

Please re-read the solution. We get (99/100)^100 NOT (99/100)*100...
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Re: M09-35 &nbs [#permalink] 31 May 2018, 22:15
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# M09-35

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