Two copies (1 & 2) are first printings, and the other three (3, 4, & 5) are seco
ID: 3205929 • Letter: T
Question
Two copies (1 & 2) are first printings, and the other three (3, 4, & 5) are second printings. Now assume two copies are to be randomly selected to be placed on 2-hour reserve (this implies 10 equally likely outcomes).
What is the probability that both selected copies are first printings?
What is the probability that both selected copies are second printings?
What is the probability that at least one selected copy is a first printing?
What is the probability that the selected copies are different printings?
Explanation / Answer
Given
Ist printing : 1,2
Ind Printings: 3,4,5
Draw 2 copies at random from 5 copies
a) The probability that both selected copies are first printings is 2C2 / 5C2 = 1 / 10 =0.1
b) The probability that both selected copies are second printings is 3C2 / 5C2 = 3 / 10 =0.3
c) The probability that atleast one selected copies from first printings is
= (2C1 3C1) / 5C2 + 2C2 / 5C2 = 1 / 10 =0.1
= 6 / 10 + 1 / 10
= 7/10 = 0.7
d) The probability that the selected copies are different printings is
= (2C1 * 3C1) / 5C2
= 6 / 10
= 0.6
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