The chance of rain in Dennyville is 40% on Monday and 80% on Tuesday.

Question

The chance of rain in Dennyville is 40% on Monday and 80% on Tuesday. What is the probability that it rains in Dennyville on at least one of these two days?

A. 120%
B. 88%
C. 76%
D. 60%
E. 32%

GMATinsight · Answer

METHOD 1:

Probability of raining on Monday = 40%
Probability of raining on Tuesday = 80%

Probability on raining one atleast one of the two days = Probability of rain on Monday + Probability of Rain on Tuesday - Probability of Raining on both days

i.e. Probability on raining one atleast one of the two days = 0.40+0.80 - (0.4*0.8) = 0.88 = 88%

ALTERNATIVE METHOD-2

Probability on raining one atleast one of the two days = 1 - (Probability of not raining on both days)  
Probability of  NOT  raining on Monday = 100-40 = 60% = 0.6
Probability of  NOT  raining on Monday = 100-80 = 20% = 0.2
i.e. Probability on raining one atleast one of the two days = 1 - (0.6*0.2) = 1- 0.12 = 0.88 = 88%

Answer: Option B

Archit3110 · Answer

GMATinsight  ;
sir , please see highlighted part

Archit3110 · Answer

no rain monday ; .6 and for tuesday ; .2
atleast rain on 1 of the days ; 1-(.6*.2) ; 1-.12 ; .88
or say 88%
IMO B

ScottTargetTestPrep · Answer

The probability that it rains on at least one day is:

P (rain at least one day) = 1 - (probability of no rain on each day)

P (rain at least one day) = 1 - 0.6 x 0.2

P (rain at least one day) = 1 - 0.12 = 0.88

Answer: B

BrentGMATPrepNow · Answer

We want P(at least one day of rain)
When it comes to probability questions involving " at least, " it's usually best to try using the  complement . 
That is, P(Event A happening) = 1 - P(Event A  not  happening)
So, here we get: P(at least one day of rain) = 1 -  P( not  getting at least one day of rain) 
What does it mean to  not  get at least one day of rain? It means getting zero rain. 
So, we can write: P(getting at least one day of rain) = 1 -  P(getting zero days of rain)

P(getting zero days of rain)  
P(getting zero days of rain) = P(no rain on Monday   AND   no rain on Tuesday)
= P(no rain on Monday)   x   P(no rain on Tuesday)

Given: P(rain on Monday) = 40% = 0.4, which means = P(NO rain on Monday) = 60% = 0.6
Given: P(rain on Tuesday) = 80% = 0.8, which means = P(NO rain on Tuesday) = 20% = 0.2

So, P(getting zero days of rain) = 0.6   x   0.2
=  0.12

So, P(getting at least one day of rain) = 1 -  0.12 
= 0.88
= 88%

Answer: B

Cheers,
Brent

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The chance of rain in Dennyville is 40% on Monday and 80% on Tuesday.

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The chance of rain in Dennyville is 40% on Monday and 80% on Tuesday.

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