Last visit was: 26 Apr 2024, 02:19 It is currently 26 Apr 2024, 02:19

Close
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
Your Progress

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.
Close
Request Expert Reply
Confirm Cancel
SORT BY:
Date
Tags:
Show Tags
Hide Tags
Math Expert
Joined: 02 Sep 2009
Posts: 92929
Own Kudos [?]: 619096 [42]
Given Kudos: 81609
Send PM
Most Helpful Reply
User avatar
Manager
Manager
Joined: 03 Sep 2014
Posts: 68
Own Kudos [?]: 146 [13]
Given Kudos: 89
Concentration: Marketing, Healthcare
Send PM
Manager
Manager
Joined: 24 Jan 2015
Posts: 56
Own Kudos [?]: 602 [7]
Given Kudos: 9
GPA: 4
WE:Consulting (Pharmaceuticals and Biotech)
Send PM
General Discussion
User avatar
Manager
Manager
Joined: 29 Mar 2015
Posts: 69
Own Kudos [?]: 45 [4]
Given Kudos: 21
Concentration: Strategy, Operations
GMAT 1: 700 Q51 V33
WE:Research (Other)
Send PM
Re: Two integers between 1 and 100, inclusive, each randomly and independe [#permalink]
1
Kudos
2
Bookmarks
Bunuel wrote:
Two integers between 1 and 100, inclusive, each randomly and independently chosen, are either added or multiplied, with an equal chance of either operation. What is the probability that the result is even?

(A) 1/3
(B) 1/2
(C) 5/8
(D) 2/3
(E) 7/8


Kudos for a correct solution.


Nos from 1-100 total 50 even, 50 odd so p(even) = p(odd) = 1/2
Cases: even+even, even*even, odd+odd, odd*even, even*odd
P(multiplication, addition) = 1/2
hence for every case Probability = 1/8 ---->(P of add / multiply * p of 1st no. * P of picking second no.) , total 5 cases so 5/8. (C)
User avatar
Senior Manager
Senior Manager
Joined: 07 Aug 2011
Posts: 425
Own Kudos [?]: 1752 [5]
Given Kudos: 75
Concentration: International Business, Technology
GMAT 1: 630 Q49 V27
Send PM
Re: Two integers between 1 and 100, inclusive, each randomly and independe [#permalink]
5
Kudos
1/2×1/2×1/2 = P (+, odd, odd)
1/2×1/2×1/2 = P (+, even, even)
1/2×1/2×1/2 = P (×, odd, even)
1/2×1/2×1/2 = P (×, even, odd)
1/2×1/2×1/2 = P (×, even, even)

5×1/2×1/2×1/2= 5/8
Manager
Manager
Joined: 03 May 2013
Posts: 95
Own Kudos [?]: 50 [1]
Given Kudos: 114
Location: India
Send PM
Re: Two integers between 1 and 100, inclusive, each randomly and independe [#permalink]
1
Kudos
Bunuel wrote:
Two integers between 1 and 100, inclusive, each randomly and independently chosen, are either added or multiplied, with an equal chance of either operation. What is the probability that the result is even?

(A) 1/3
(B) 1/2
(C) 5/8
(D) 2/3
(E) 7/8


Kudos for a correct solution.

Hi experts , please shed some light ,

first of all by picking randomly , I think it is talking abt without replacement, which means P of selecting first even no - 50/100 then second 49/99(not again 50/100)

second;- why double counted sets are not subtracted , for example picking 40 and 42 give even result whether the opreation may be app or multiply , hence it should counted once only and in every solution it is counted twice.

in my opinion the sol should be(considering with replacement) [1/2 {ee(even,even)+oo(odd,odd)} + 1/2 (eo+oe+ee) - ee]
RC & DI Moderator
Joined: 02 Aug 2009
Status:Math and DI Expert
Posts: 11179
Own Kudos [?]: 31937 [2]
Given Kudos: 290
Send PM
Re: Two integers between 1 and 100, inclusive, each randomly and independe [#permalink]
2
Kudos
Expert Reply
vipulgoel wrote:
Bunuel wrote:
Two integers between 1 and 100, inclusive, each randomly and independently chosen, are either added or multiplied, with an equal chance of either operation. What is the probability that the result is even?

(A) 1/3
(B) 1/2
(C) 5/8
(D) 2/3
(E) 7/8


Kudos for a correct solution.

Hi experts , please shed some light ,

first of all by picking randomly , I think it is talking abt without replacement, which means P of selecting first even no - 50/100 then second 49/99(not again 50/100)

second;- why double counted sets are not subtracted , for example picking 40 and 42 give even result whether the opreation may be app or multiply , hence it should counted once only and in every solution it is counted twice.

in my opinion the sol should be(considering with replacement) [1/2 {ee(even,even)+oo(odd,odd)} + 1/2 (eo+oe+ee) - ee]


hi,
1) concerning your first doubt , the two numbers are picked up independent of each other so the same number can be picked up twice..
2) secondly each multiplication operation is different from and independent of add operation and possiblity of add or multiplication is 1/2 so you have to take event separately even if the two operations lead to same outcome
hope it helped
Manager
Manager
Joined: 03 May 2013
Posts: 95
Own Kudos [?]: 50 [0]
Given Kudos: 114
Location: India
Send PM
Re: Two integers between 1 and 100, inclusive, each randomly and independe [#permalink]
chetan2u wrote:
vipulgoel wrote:
Bunuel wrote:
Two integers between 1 and 100, inclusive, each randomly and independently chosen, are either added or multiplied, with an equal chance of either operation. What is the probability that the result is even?

(A) 1/3
(B) 1/2
(C) 5/8
(D) 2/3
(E) 7/8


Kudos for a correct solution.

Hi experts , please shed some light ,

first of all by picking randomly , I think it is talking abt without replacement, which means P of selecting first even no - 50/100 then second 49/99(not again 50/100)

second;- why double counted sets are not subtracted , for example picking 40 and 42 give even result whether the opreation may be app or multiply , hence it should counted once only and in every solution it is counted twice.

in my opinion the sol should be(considering with replacement) [1/2 {ee(even,even)+oo(odd,odd)} + 1/2 (eo+oe+ee) - ee]


hi,
1) concerning your first doubt , the two numbers are picked up independent of each other so the same number can be picked up twice..
2) secondly each multiplication operation is different from and independent of add operation and possiblity of add or multiplication is 1/2 so you have to take event separately even if the two operations lead to same outcome
hope it helped


Thanks for the prompt response about #2 i m still skeptical , i understand operations are different , but if outcome is coming out same twice then why we are not subtracting , ne how we are concerned with final outcome,
Manager
Manager
Joined: 31 Jul 2017
Posts: 73
Own Kudos [?]: 96 [0]
Given Kudos: 474
Location: India
Send PM
Re: Two integers between 1 and 100, inclusive, each randomly and independe [#permalink]
Hi VeritasKarishma , chetan2u

I am unable to understand how can we have 8 possible combinations ?

(Even,odd) (Odd,odd) or (Even,Even)

Considering addition or Multiplication , total combination is 6 and no of cases in which we will get even is 6, making it 2/3.

Even we are picking up the same no again, aren't they covered as a part of (e,e) or (o,o) ?
Please help.
RC & DI Moderator
Joined: 02 Aug 2009
Status:Math and DI Expert
Posts: 11179
Own Kudos [?]: 31937 [0]
Given Kudos: 290
Send PM
Re: Two integers between 1 and 100, inclusive, each randomly and independe [#permalink]
Expert Reply
Manas1212 wrote:
Hi VeritasKarishma , chetan2u

I am unable to understand how can we have 8 possible combinations ?

(Even,odd) (Odd,odd) or (Even,Even)

Considering addition or Multiplication , total combination is 6 and no of cases in which we will get even is 6, making it 2/3.

Even we are picking up the same no again, aren't they covered as a part of (e,e) or (o,o) ?
Please help.


What you are missing out is (odd,even) is different from (even,odd)..
So (Odd,even), (Even,odd) (Odd,odd) or (Even,Even) are 4 different possibilities..
Both operations have equal chance so 1/2..
Addition ..
Out of 4 possibilities, 2 will result in odd and 2 in even..
So probability is (1/2)*(2/4)=1/4
Multiplication..
Out of possibilities, only 1 will result in odd when both are odd.
So probability is (1/2)*(3/4)=3/8

Total probability is 1/4+3/8=5/8

C
Manager
Manager
Joined: 15 Nov 2020
Posts: 99
Own Kudos [?]: 13 [0]
Given Kudos: 1614
Send PM
Re: Two integers between 1 and 100, inclusive, each randomly and independe [#permalink]
Bunuel wrote:
Two integers between 1 and 100, inclusive, each randomly and independently chosen, are either added or multiplied, with an equal chance of either operation. What is the probability that the result is even?

(A) 1/3
(B) 1/2
(C) 5/8
(D) 2/3
(E) 7/8


Kudos for a correct solution.


I tried doing this way- 1- (1/2*(50c2+2!(50c1*50c1))/100c2)

50c2- Choosing from the set of odd numbers
50c1- Choosing each from the set of odd numbers and even numbers

Where am I going wrong? Please help
User avatar
Intern
Intern
Joined: 15 Nov 2022
Posts: 3
Own Kudos [?]: [0]
Given Kudos: 5
Location: Myanmar
GMAT 1: 550 Q40 V40
Send PM
Re: Two integers between 1 and 100, inclusive, each randomly and independe [#permalink]
I am confusing multiplication of 1/2 in 3 times for picking two integers.
Thus means, the probability of (Odd + Odd) = 1/2 * 1/2 = 1/4 (not 1/8).
Please kindly answer me if you get the answer. Thank you..
Math Expert
Joined: 02 Sep 2009
Posts: 92929
Own Kudos [?]: 619096 [1]
Given Kudos: 81609
Send PM
Re: Two integers between 1 and 100, inclusive, each randomly and independe [#permalink]
1
Kudos
Expert Reply
theint481 wrote:
I am confusing multiplication of 1/2 in 3 times for picking two integers.
Thus means, the probability of (Odd + Odd) = 1/2 * 1/2 = 1/4 (not 1/8).
Please kindly answer me if you get the answer. Thank you..


Check the solution below, hope it answers your question.

Two integers between 1 and 100, inclusive, each randomly and independently chosen, are either added or multiplied, with an equal chance of either operation. What is the probability that the result is even?

(A) 1/3
(B) 1/2
(C) 5/8
(D) 2/3
(E) 7/8


1. The sum of two integers to be even, both of them must be even or both of them must be odd. Therefore, the probability of the sum to be even is:

    P(the even sum) = P(even, even) + P(odd, odd) = 1/2*1/2 + 1/2*1/2 = 1/2.

2. The product of two integers to be even, either of them or both must be even. Therefore, the probability of the product to be even is:

    P(the even product) = P(even, odd) + P(odd, even) + P(even, even) = 1/2*1/2 + 1/2*1/2 + 1/2*1/2 = 3/4.

In half of the cases we have summation and in half of the cases we have multiplication, therefore the overall probability is:

    P(even result) = 1/2*1/2 + 1/2*3/4 = 5/8.

Answer: C.

Or another approach.

Let's calculate the probability that the result is odd and subtract that from 1.

1. The sum of two integers to be odd, one of the integers must be odd and another even. Therefore, the probability of the sum to be odd is:

    P(the odd sum) = P(even, odd) + P(odd, even) = 1/2*1/2 + 1/2*1/2 = 1/2.

2. The product of two integers to be odd, both must be odd. Therefore, the probability of the product to be odd is:

    P(the odd product) = P(odd, odd) = 1/2*1/2 = 1/4.

In half of the cases we have summation and in half of the cases we have multiplication, therefore the overall probability that the result is odd is:

    P(odd result) = 1/2*1/2 + 1/2*1/4 = 3/8.

Therefore, the probability that the result is even is:

    P(even result) = 1 - P(odd result) = 1 - 3/8 = 5/8.

Answer: C.

Hope it's clear.
GMAT Club Bot
Re: Two integers between 1 and 100, inclusive, each randomly and independe [#permalink]
Moderators:
Math Expert
92921 posts
Senior Moderator - Masters Forum
3137 posts

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne