BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

DS - Probability - 5 - spinner spunning

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
User avatar
Legendary Member
Posts: 1665
Joined: Thu Nov 03, 2011 7:04 pm
Thanked: 165 times
Followed by:70 members

DS - Probability - 5 - spinner spunning

by karthikpandian19 » Tue Jul 24, 2012 5:15 am
A certain spinner can land in one of four regions, each of which is labeled with a different positive integer less than or equal to 10. On any spin, there is an equal probability of landing on any of the four regions. If the spinner is spun twice in a row, what is the probability that the sum of the two spins is odd?

1. If the spinner is spun twice, the probability that the product of the two spins will be odd is zero.
2. No region on the spinner is labeled with a prime number.
Regards,
Karthik
The source of the questions that i post from JUNE 2013 is from KNEWTON

---If you find my post useful, click "Thank" :) :)---
---Never stop until cracking GMAT---
Top
Source: — Data Sufficiency |
Master | Next Rank: 500 Posts
Posts: 156
Joined: Sun Jul 15, 2012 12:03 pm
Location: New York, USA
Thanked: 34 times
Followed by:1 members

by kartikshah » Tue Jul 24, 2012 5:52 am
I think A should be sufficient here.
The regions can be 1,2,3,4,5,6,7,8,9
If the spinner is spun twice then the product of the two spins can be:
E*E = E
E*O =E
O*E =O
O*O = O
Since the product can never be odd, the last possibility is eliminated.

So the sum can be:
E+E = E
E+O=O
O+E=O

Probability should be 2/3
Top
User avatar
Master | Next Rank: 500 Posts
Posts: 210
Joined: Thu Mar 08, 2012 11:24 pm
Thanked: 62 times
Followed by:3 members

by niketdoshi123 » Tue Jul 24, 2012 6:16 am
karthikpandian19 wrote:A certain spinner can land in one of four regions, each of which is labeled with a different positive integer less than or equal to 10. On any spin, there is an equal probability of landing on any of the four regions. If the spinner is spun twice in a row, what is the probability that the sum of the two spins is odd?

1. If the spinner is spun twice, the probability that the product of the two spins will be odd is zero.
2. No region on the spinner is labeled with a prime number.
Statement 1: INSUFFICIENT

If the product of the 2 spins will not be odd, this means that at least 3 regions are labelled with even numbers.
So we will get diff probability in the following two cases
1) there is no odd integer i.e there are 4 even integers.
2) there is 1 odd integer & are 3 even integers.

Statement 2:INSUFFICIENT
Prime numbers <= 10
2,3,5,7
The integers, which can be labelled, should be among 1,4,6,8,9,10

There are 2 odd integers and 4 even integers
Possible cases, which will give different probabilities are as follows:
1) 2 odd & 2 even integers
2) 1 odd & 3 even integers
3) 0 odd & 4 even integers

Combining both the statements

from statement 2 we know that there are 4 even integers, which can be labelled in 4 different regions and will still satisfy statement 1
and labeling regions with 1 odd and 3 even integers will also satisfy both the statements.

Hence the answer is E
Top
User avatar
Legendary Member
Posts: 520
Joined: Sat Apr 28, 2012 9:12 pm
Thanked: 339 times
Followed by:49 members
GMAT Score:770

by eagleeye » Tue Jul 24, 2012 6:32 pm
karthikpandian19 wrote:A certain spinner can land in one of four regions, each of which is labeled with a different positive integer less than or equal to 10. On any spin, there is an equal probability of landing on any of the four regions. If the spinner is spun twice in a row, what is the probability that the sum of the two spins is odd?

1. If the spinner is spun twice, the probability that the product of the two spins will be odd is zero.
2. No region on the spinner is labeled with a prime number.
We are given a spinner which can land in r regions, each marked with a different number between 1 and 10 inclusive. We need to find whether we can determine the probability of the sums of spins being odd. Sum of spins will be odd if and only if one spin lands on an even number and the other lands on an odd number. With this in mind, let's look at the statements:

1. If the spinner is spun twice, the probability that the product of the two spins will be odd is zero.
Product is odd only when both numbers are odd. If the probability of landing at an odd number in both spins is 0, it only means one thing. It means that there are no odd numbers present (Even if there was just one odd number present, the spinner could land on the same odd number twice and resulted in an odd product. The fact that it NEVER happens tells us that there are no odd numbers on the spinner).
In that case, probability of an odd sum = 0. Sufficient.

2. No region on the spinner is labeled with a prime number.
The primes between 1 and 10 are 2,3,5 and 7.
The non-primes are 1,4,6,8,9,10.
If there are no prime numbers, we can have any four numbers from the non-primes.
If they are 4,6,8,10. probability of odd sum = 0.
If they are 1,4,6,9. probability of odd sum is not 0.
Insufficient.

A is the correct answer.
Top
Post new topic Post Reply
• Page 1 of 1