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#### Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here. # The probability of rain in Greg’s town on Tuesday is 0.3. Th  Question banks Downloads My Bookmarks Reviews Important topics
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Retired Moderator Joined: 07 Jun 2014
Posts: 4803
GRE 1: Q167 V156 WE: Business Development (Energy and Utilities)
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Kudos [?]: 2922 , given: 394

The probability of rain in Greg’s town on Tuesday is 0.3. Th [#permalink]
Expert's post 00:00

Question Stats: 54% (00:42) correct 45% (00:47) wrong based on 44 sessions
The probability of rain in Greg’s town on Tuesday is 0.3. The probability that Greg’s teacher will give him a pop quiz on Tuesday is 0.2. The events occur independently of
each other.

 Quantity A Quantity B The probability that either or both events occur The probability that neither event occurs

A) Quantity A is greater.
B) Quantity B is greater.
C) The two quantities are equal.
D) The relationship cannot be determined from the information given.
[Reveal] Spoiler: OA

_________________

Sandy
If you found this post useful, please let me know by pressing the Kudos Button

Try our free Online GRE Test Retired Moderator Joined: 07 Jun 2014
Posts: 4803
GRE 1: Q167 V156 WE: Business Development (Energy and Utilities)
Followers: 171

Kudos [?]: 2922  , given: 394

Re: The probability of rain in Greg’s town on Tuesday is 0.3. Th [#permalink]
3
KUDOS
Expert's post
Explanation

The problem indicates that the events occur independently of each other. Therefore, in calculating Quantity A, do not just add both events, even though it is an “or” situation. Adding 0.3 + 0.2 = 0.5 is incorrect because the probability that both events occur is counted twice. (Only add probabilities in an “or” situation when the probabilities are mutually exclusive.)

While Quantity A’s value should include the probability that both events occur, make sure to count this probability only once, not twice. Since the probability that both events occur is 0.3(0.2) = 0.06, subtract this value from the “or” probability.

Quantity A: Add the two probabilities (rain or pop quiz) and subtract both scenarios (rain and pop quiz): 0.3 + 0.2 – (0.3)(0.2) = 0.44
Quantity B: Multiply the probability that rain does not occur (0.7) and the probability that the pop quiz does not occur (0.8): 0.7(0.8) = 0.56

Alternatively, note that the two quantities, collectively, include every possibility and are mutually exclusive of one another (Quantity A includes “rain and no quiz,” “quiz and no rain,” and “both rain and quiz,” and Quantity B includes “no rain and no quiz”). Therefore, the values of Quantities A and B must sum to 1. Calculating the value of either Quantity A or Quantity B would automatically indicate the value for the other quantity.

If you do this, calculate Quantity B first (because it’s the easier of the two quantities to calculate) and then subtract Quantity B from 1 in order to get Quantity A’s value. That is, 1 – 0.56 = 0.44.
_________________

Sandy
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Try our free Online GRE Test Re: The probability of rain in Greg’s town on Tuesday is 0.3. Th   [#permalink] 21 Aug 2018, 18:31
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