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21 Jun 2022, 13:45
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E
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
15%
(low)
Question Stats:
80% (00:36) correct
20%
(00:31)
wrong
based on 51
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3 coins are tossed simultaneously, what is the probability of getting at least one tail ?
A. 1/8
B. 3/8
C. 1/2
D. 5/8
E. 7/8
A. 1/8
B. 3/8
C. 1/2
D. 5/8
E. 7/8
21 Jun 2022, 18:08
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Sometimes, in combinatorics and probability is better go after you don’t want when what you want gives you more trouble.
If you are working with mutually exclusive sets and this expression “at least one” be aware and check if the technique presented applies.
If you are working with mutually exclusive sets and this expression “at least one” be aware and check if the technique presented applies.
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21 Jun 2022, 21:03
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Bunuel
We can either calculate the probability of "winning" or we can calculate the probability of "losing" and subtract from 1. Losing is easier, so let's do that way. Quick tip: since we know that we will have some little step at the end to convert from losing to winning, I like to flip my computer mouse over as I start working the problem. That way, I have a reminder in case I'm about to click an answer and have forgotten that last step...after all, I'm willing to bet that one of the answer choices is going to be the probability of "losing."
Okay, let's solve. The only way to lose is HHH. The probability of that outcome is 1/2 * 1/2 * 1/2 - 1/8.
Probability of winning is 1-losing, so 1 - 1/8 = 7/8.
Answer choice E.
