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15 Apr 2025, 00:30
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A
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Difficulty:
95%
(hard)
Question Stats:
36% (02:24) correct
64%
(01:39)
wrong
based on 104
sessions
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Every time Brad goes surfing his probability of suffering a shark bite is p. How many times can Brad go surfing before his probability being bitten at least once is more than 90% ?
(1) p = 1/3
(2) Brad's probability of suffering his first shark bite on his second time surfing is 2/9.
(1) p = 1/3
(2) Brad's probability of suffering his first shark bite on his second time surfing is 2/9.
15 Apr 2025, 12:01
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Bunuel
Probability of Brad suffering a shark bite is p,
Probability of not suffering a shark bite = 1-p.
We need to find : How many times can Brad go surfing before his probability being bitten at least once is more than 90% ?
This can be rephrased as probability of Brad NOT being bitten atleast once is less than 10%.
Statement 1:
(1) p = 1/3
Not bitten = 1-1/3 = 2/3.
(2/3)^n < 0.10
When n = 6, left hand side becomes less than 0.10. Hence, Statement 1 is sufficient.
Statement 2:
(2) Brad's probability of suffering his first shark bite on his second time surfing is 2/9.
Brad suffered shark bite during the second time, first time he did not encounter shark bite.
(1-p) * p = 2/9
p- p^2 =2/9
9p- 9p^2 =2
9p^2 - 9p +2 =0
Solving it we get two values of P (2/3 and 1/3).
we will get two different values of n. Hence, not sufficient.
Option A
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