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The probability that event M will not occur is 0.8 and the probability

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Joined: 12 Sep 2018
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Re: The probability that event M will not occur is 0.8 and the probability  [#permalink]

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New post 24 Oct 2018, 17:13
mskx wrote:
How to you calculate P(M and R) that you get 0?

or means add
and means multiply

To stay with your example:
P(M or R) = P(M) + P(R) - P(M and R)
P(M or R) = P(0.9) + P(0.9) - P(0.9*0.9) -> 0.9*0.9 is not 0
But please consider that P(M or R) = P(M) + P(R) -P(M and R) is wrong because its a mutually exclusive event.


Because they're mutually exclusive, P(M and R) can't happen. That's why I used 0. So really it's P(M or R)=P(M) + P(R). If P(M) and P(R) are each 0.9 (mutually exclusive of course), the P(M or R) becomes 1.8, which is what doesn't make sense to me.
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Re: The probability that event M will not occur is 0.8 and the probability  [#permalink]

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New post 25 Oct 2018, 00:19
M will not occur = 0.8
M will occur = 0.2

R will not occur = 0.6
R will occur = 0.4

Probability that either event M or event R will occur = 0.2 + 0.4 = 0.6 (3/5)

Hence C
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Re: The probability that event M will not occur is 0.8 and the probability  [#permalink]

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New post 26 Jan 2019, 10:10
Dear experts,
P(M)=.8, Hence P(M')=.2
P(R)=.6, So P(R')=.4
P(Either of the events)=P(M' and R) OR P(R' and M)=(.2*.6)+(.8*.4)=.44.

Can some one please explain what I am missing here.

Regards,
Arup
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Re: The probability that event M will not occur is 0.8 and the probability  [#permalink]

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New post 26 Jan 2019, 10:31
2
Bunuel wrote:
The probability that event M will not occur is 0.8 and the probability that event R will not occur is 0.6. If events M and R cannot both occur, which of the following is the probability that either event M or event R will occur?

A) 1/5
B) 2/5
C) 3/5
D) 4/5
E) 12/25


I will use the 2*2 matrix here

MO= M will occur
MNO= M will not occur

All the values are given, and we need to find

--------MO--------MNO
-RO----0----------0.4-----0.4
RNO---0.2--------0.4-----0.6
-------0.2---------0.8------1

either event M or event R will occur, this will be again => 1 - (both will occur), Since in probability P(happening) + P(not happening) = 1
1-0.4 =0.6

C
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If you notice any discrepancy in my reasoning, please let me know. Lets improve together.

Quote which i can relate to.
Many of life's failures happen with people who do not realize how close they were to success when they gave up.
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Re: The probability that event M will not occur is 0.8 and the probability  [#permalink]

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New post 10 May 2019, 11:02
shonakshi wrote:
Can someone please explain why is it not
0.8*0.4+0.2*0.6
11/25
:?


This is not right as you are confusing between Event and Occurrence of the event. Your formula would be true if you try to find out, probability of EXACTLY one of M or R will occur, when the other WILL NOT occur. This is NOT same as 'probability of M or R to occur'.
I will illustrate with an example. Scenario 1: You are tossing a coin 2 times. What's the probability of getting EXACTLY one head? Your above formula will work in this case. There are 2 occurrences of toss here. Also, P(H) = 1/2 and P(T) = 1/2. Get EXACTLY one head in two tosses = P(H).P(~T) + P(~H).P(T) = 1/2. [without formula: HT (valid), TH (valid), HH (invalid), TT (invalid). Hence : 2/4 = 1/2]
Scenario 2: What is the probability of getting a head OR tail when you toss a coin? Note: here it is talking about only one occurrence of toss. Here the formula should be P(H or T) = P(H) + P(T) - P(H and T). P(H and T) is obviously 0. So, P(H or T) = 1/2 + 1/2 = 1 (it's a certainty). [now without formula: it is a guarantee in a coin toss that you will either get head or tail. so, probability = 1 ]

This question in OP is the second scenario described above, hence your formula won't give you correct result. Hope it helps !!
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Re: The probability that event M will not occur is 0.8 and the probability  [#permalink]

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New post 10 May 2019, 11:58
Bunuel wrote:
The probability that event M will not occur is 0.8 and the probability that event R will not occur is 0.6. If events M and R cannot both occur, which of the following is the probability that either event M or event R will occur?

A) 1/5
B) 2/5
C) 3/5
D) 4/5
E) 12/25


M will occur =1-.8=.2
R will occur =1-.6=.4

P(M or R)=P(M)+P(R)-P(M & R)
=.2+.4-0
=.6=3/5

Answer is C

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Re: The probability that event M will not occur is 0.8 and the probability   [#permalink] 10 May 2019, 11:58

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