Problem Solving

Hi LUANDATO,

We're told that the probability of Sita getting selected to any individual school is 20% and that she applied to 3 schools. We're asked for the probability that she will get selected to AT LEAST one school.

With these types of probability questions, it's often easiest to calculate the probability of what you DON'T WANT - and then subtract that fraction from 1 to determine the probability of what you DO want. The question asks for the probability that she will get selected to AT LEAST one school, so we'll calculate the probability that she will get selected to 0 schools. A 20% chance of getting selected means an 80% chance of NOT getting selected. Since the answers are fractions, we should write 80% as 4/5:

(Not selected)(Not selected)(Not selected) = (4/5)(4/5)(4/5) = 64/125 chance of getting selected by 0 schools

Thus, he probability that she will get selected to AT LEAST one school is... 1 - 64/125 = 61/125

Final Answer: C

GMAT assassins aren't born, they're made,
Rich

LUANDATO wrote:If the probability of Sita getting selected to a school is 20% and she applied to 3 schools. What is the probability that she will get selected in at least one school?

A. 24/125
B. 21/125
C. 61/125
D. 12/125
E. 18/125

We can use the equation:

P(selected into at least 1 school) = 1 - P(selected to no schools)

P(selected to no schools) = 4/5 x 4/5 x 4/5 = 64/125

Thus,

P(selected into at least 1 school) = 1 - 64/125 = 61/125

Answer: C