Clases GMATHome > GMAT Focus Edition Data Insight QUESTION > Data Sufficiency > Probability > A fish tank contains a number of fish, including 5 Fantails. If two fish (...)
A fish tank contains a number of fish, including 5 Fantails. If two fish are selected from the tank at random, what is the probability that both will be Fantails?
Difficulty: 600-700 Level, Probability, Data Sufficiency (DS)
Monday 25 July 2022, by
A fish tank contains a number of fish, including 5 Fantails. If two fish are selected from the tank at random, what is the probability that both will be Fantails?
(1) The probability that the first fish chosen will be a Fantail is 1/2.
(2) If the first selected fish is a Fantail, then the probability the second selection is also a Fantail is 4/9
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EXPLANTION:
Statement 1: This choice says that the no. of fish=5, The probability of Fantail=5/10=1/2. Sufficient.
Statement 2:
Let the no. of fish=x,
1.Prob of first (Fish)+ Prob of second (Fantail) Or
2. Prob of both(Fantail)
1.[(x/x+5)]*[(x-1)/(x+5-1)]=4/9.
x is not an integer. (NOT POSSIBLE)
2. This gives x=5.(Only Possible Value).
Therefore the answer is Option D.