Join us for MBA Spotlight – The Top 20 MBA Fair      Schedule of Events | Register

 It is currently 04 Jun 2020, 12:39 ### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

#### Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.  # The probability that event M will not occur is 0.8 and the probability

Author Message
TAGS:

### Hide Tags

Intern  B
Joined: 12 Sep 2018
Posts: 3
Location: United States
Schools: HBS '22 (S)
GMAT 1: 750 Q49 V44
GPA: 3.6
Re: The probability that event M will not occur is 0.8 and the probability  [#permalink]

### Show Tags

mskx wrote:
How to you calculate P(M and R) that you get 0?

and means multiply

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.
Manager  S
Joined: 24 Dec 2017
Posts: 180
Location: India
Concentration: Strategy, Real Estate
Schools: Johnson '21
Re: The probability that event M will not occur is 0.8 and the probability  [#permalink]

### Show Tags

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
Manager  G
Joined: 23 Jan 2018
Posts: 228
Location: India
WE: Information Technology (Computer Software)
Re: The probability that event M will not occur is 0.8 and the probability  [#permalink]

### Show Tags

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
Director  G
Joined: 09 Mar 2018
Posts: 980
Location: India
Re: The probability that event M will not occur is 0.8 and the probability  [#permalink]

### Show Tags

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
_________________
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.
Intern  B
Joined: 23 Aug 2016
Posts: 14
Re: The probability that event M will not occur is 0.8 and the probability  [#permalink]

### Show Tags

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 !!
Manager  B
Joined: 25 Sep 2018
Posts: 65
Re: The probability that event M will not occur is 0.8 and the probability  [#permalink]

### Show Tags

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

Posted from my mobile device
Intern  B
Joined: 31 Oct 2018
Posts: 3
Location: Switzerland
Schools: Tsinghua
GPA: 3.25
WE: Sales (Consumer Products)
Re: The probability that event M will not occur is 0.8 and the probability  [#permalink]

### Show Tags

After months of just reading this forum's precious advice, I'll give it a go and ask a question for the first time.

Just went through all the OG questions, and this one was the earliest that messed with my mind:

My Idea is that the Probability that neither A nor B occurs is 0.6 x 0.8 = 0.48 the rest 0.52 (minus the Probability that both occur, = 0) is the result.

Can someone explain why that approach is wrong.

Thanks
Intern  B
Joined: 23 Nov 2018
Posts: 28
The probability that event M will not occur is 0.8 and the probability  [#permalink]

### Show Tags

A lot of users have tried explaining why
0.8*0.4+0.2*0.6
11/25
is wrong, but I think the confusion still stands

We understand why the correct soln is correct but we don't understand why our soln is incorrect. Can you help us bridge the gap?
Thanks for your time and help Math Expert V
Joined: 02 Aug 2009
Posts: 8623
Re: The probability that event M will not occur is 0.8 and the probability  [#permalink]

### Show Tags

2
legendinthewomb wrote:

A lot of users have tried explaining why
0.8*0.4+0.2*0.6
11/25
is wrong, but I think the confusion still stands

We understand why the correct soln is correct but we don't understand why our soln is incorrect. Can you help us bridge the gap?
Thanks for your time and help Hi

It is given that both events A and B will NOT occur together, so when you take one occurring say A =0.4, other B NOT occurring is not 0.8, it is 1 or 100% because it is sure that B will not occur when A is occurring. So answer is 0.2+0.4=0.6
Say you have only 20 cards of a pack of 52 cards. Probability of picking not picking an A is 0.9 and probability of not picking King is 0.8.
Probability of picking any one will be straight sum of individual probabilities that is 0.1+0.2 because they cannot occur together.
_________________
Intern  B
Joined: 23 Nov 2018
Posts: 28
Re: The probability that event M will not occur is 0.8 and the probability  [#permalink]

### Show Tags

chetan2u wrote:
legendinthewomb wrote:

A lot of users have tried explaining why
0.8*0.4+0.2*0.6
11/25
is wrong, but I think the confusion still stands

We understand why the correct soln is correct but we don't understand why our soln is incorrect. Can you help us bridge the gap?
Thanks for your time and help Hi

It is given that both events A and B will NOT occur together, so when you take one occurring say A =0.4, other B NOT occurring is not 0.8, it is 1 or 100% because it is sure that B will not occur when A is occurring. So answer is 0.2+0.4=0.6
Say you have only 20 cards of a pack of 52 cards. Probability of picking not picking an A is 0.9 and probability of not picking King is 0.8.
Probability of picking any one will be straight sum of individual probabilities that is 0.1+0.2 because they cannot occur together.

Got it! Basically we misunderstood the question (or question doesn't have as much clarity as we'd like it to have).

It means: Only one event can be happen regardless of whether it fails or not.
What it doesn't mean: Both these events can't happen simultaneously ie both of them succeeding at the same time. They can occur simultaneously but only one event can be successful.
GMAT Club Legend  V
Joined: 18 Aug 2017
Posts: 6314
Location: India
Concentration: Sustainability, Marketing
GPA: 4
WE: Marketing (Energy and Utilities)
Re: The probability that event M will not occur is 0.8 and the probability  [#permalink]

### Show Tags

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 not occur- 0.8 and will occur = .2
R will not occur = .6 and will occur = .4
either event M or event R will occur
.2+.4 ; .6 ; 6/10 ; 3/5
IMO C
CEO  V
Joined: 03 Jun 2019
Posts: 2935
Location: India
GMAT 1: 690 Q50 V34 WE: Engineering (Transportation)
Re: The probability that event M will not occur is 0.8 and the probability  [#permalink]

### Show Tags

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

The probability that event M will occur is 0.2
The probability that event R will occur is 0.4

The probability that either event M or event R will occur = .2 + .4 = .6 = 3/5 since events M and R cannot both occur

IMO C
_________________
Kinshook Chaturvedi
Email: kinshook.chaturvedi@gmail.com
CEO  V
Joined: 03 Jun 2019
Posts: 2935
Location: India
GMAT 1: 690 Q50 V34 WE: Engineering (Transportation)
The probability that event M will not occur is 0.8 and the probability  [#permalink]

### Show Tags

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
[/quote]

The probability that event M will occur is 1-.8 = 0.2
The probability that event R will occur is 1- .6 = 0.4

The probability that either event M or event R will occur = .2 + .4 = .6 = 3/5 since events M and R cannot both occur

IMO C
_________________
Kinshook Chaturvedi
Email: kinshook.chaturvedi@gmail.com
Intern  B
Joined: 18 Jul 2018
Posts: 30
The probability that event M will not occur is 0.8 and the probability  [#permalink]

### Show Tags

My mistake:

I misunderstood "M and R cannot both occur" as calculating for P(M)+P(R)-2*P(M & R), instead of thinking M & R as mutually exclusive events and therefore P(M & R) = 0.
Manager  G
Joined: 13 Nov 2018
Posts: 110
Location: India
GMAT 1: 700 Q51 V32
Re: The probability that event M will not occur is 0.8 and the probability  [#permalink]

### Show Tags

Easy one -testing concept of mutually exclusive events in probability
P(R) = 1 - 0.8= 0.2
P(M) = 1 -0.6 = 0.4

Both events cannot occur simultaneously, so r and m are mutually exclusive

Prob that either event M or event R will occur = 0.2+0.4 = 0.6 = 6/10 = 3/5
GMAT Club Legend  V
Status: GMATINSIGHT Tutor
Joined: 08 Jul 2010
Posts: 4049
Location: India
GMAT: QUANT EXPERT
Schools: IIM (A)
GMAT 1: 750 Q51 V41
WE: Education (Education)
Re: The probability that event M will not occur is 0.8 and the probability  [#permalink]

### Show Tags

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

Solution attached
Attachments Screenshot 2020-02-04 at 11.02.12 AM.png [ 245.52 KiB | Viewed 287 times ]

_________________
Prosper!!!
GMATinsight .............(Bhoopendra Singh and Dr.Sushma Jha)
e-mail: info@GMATinsight.com l Call : +91-9999687183 / 9891333772
One-on-One Skype classes l Classroom Coaching l On-demand Quant course l Admissions Consulting
Check website for most affordable Quant on-Demand course 2000+ Qns (with Video explanations)
Our SUCCESS STORIES: From 620 to 760 l Q-42 to Q-49 in 40 days l 590 to 710 + Wharton l
ACCESS FREE GMAT TESTS HERE:22 FREE (FULL LENGTH) GMAT CATs LINK COLLECTION
Intern  B
Joined: 25 Sep 2019
Posts: 9
Re: The probability that event M will not occur is 0.8 and the probability  [#permalink]

### Show Tags

Abhishek009 wrote:
shonakshi wrote:
Can someone please explain why is it not
0.8*0.4+0.2*0.6
11/25 https://people.richland.edu/james/lectu ... 5-rul.html

Hope that helps..

dude... thank you so much. so helpful Re: The probability that event M will not occur is 0.8 and the probability   [#permalink] 27 May 2020, 14:59

Go to page   Previous    1   2   [ 37 posts ]

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