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This question should be tackled using the AD/BCE strategy which is that we first explore option A. If option A is sufficient, it is possible both A AND B are sufficient, hence D can be the answer. IF A is not sufficient, D cannot be an answer and we can directly evaluate B. If B is not sufficient, try to evaluate the a combination of the two is sufficient. If yes, answer is C. If not, the answer is E.

In this question, it is clear that we need to know the range of the numbers so that one can evaluate the probability.
Option A provides this information while option B does not.

Answer is A.
Bunuel
Ann and Bob each randomly select an integer from the integers x to y, inclusive. What is the probability that the integer Ann selects is greater than the one Bob selects?

(1) y - x = 9
(2) y = -20


 


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Statement (1): y−x=9y - x = 9y−x=9
So, the range has:
y−x+1=9+1=10 integersy - x + 1 = 9 + 1 = 10 \text{ integers}y−x+1=9+1=10 integers
Perfect! That tells us exactly how many options Ann and Bob can pick from.
We don’t care what the numbers actually are, just how many.
Sufficient.

Statement (2): y=−20y = -20y=−20
Hmm... this gives us the end of the range, but nothing about x. Could be:

x = -30 gives 11 numbers
x = -100 gives 81 numbers
x = -20 gives only 1 number
So the size of the range could change wildly, and that affects the probability.
Not sufficient.

Bunuel
Ann and Bob each randomly select an integer from the integers x to y, inclusive. What is the probability that the integer Ann selects is greater than the one Bob selects?

(1) y - x = 9
(2) y = -20


 


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Statement 1
y−x=9
This means Ann and Bob are picking numbers from a list of 10 numbers, Since both are picking randomly, there are 100 possible combinations
So, there are 100 total pairs. enough to calculate the probability
so, Statement (1) is enough

Statement 2
y=−20y
This only tells us the end point, not how many numbers are in the list
Without knowing the full range, we can’t calculate the probability
so, Statement (2) is not enough.

Bunuel
Ann and Bob each randomly select an integer from the integers x to y, inclusive. What is the probability that the integer Ann selects is greater than the one Bob selects?

(1) y - x = 9
(2) y = -20


 


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Inclusive counting rule is y-x+1 so using first option we know we have 10 digits and total ways of selecting would be 10 * 10 as two players are selecting now for the one digit to be greater than other always we can select in 10*9/2 ways which means we have 45 such pairs

so probability is 45/100 which can be answered from choice 1 but choice 2 cant tell you anything about the range so option A
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target
P(A)> P(B)
#1
y-x=9
we know x, y are integers so there will always be 10 integers
P of picking a number is 1/10
P of picking another number 1/9
supposedly if list of numbers is 2 to 11
B picks 7 , for A to select number greater than B is 8,9,10,11 ; 1/5
if B picks 9 then for A to choose number greater than B is 1/2
so insufficient to determine
#2
y=-20
range is not clear
from 1 &2
range is -20 to -29
we will have same issue as discussed in #1

OPTION E is correct
Bunuel
Ann and Bob each randomly select an integer from the integers x to y, inclusive. What is the probability that the integer Ann selects is greater than the one Bob selects?

(1) y - x = 9
(2) y = -20


 


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for the GMAT Club Olympics Competition

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We are given that ann and and bob randomly chooses integers from x to y inclusive
1) when y-x =9
This means we have total 10 integers
While choosing integers half of the time ann will be greater and half time bob will be greater
This is sufficient
2) y = -20
No information on x hence not sufficient
Hence the answer is A
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It is given that: A and B select an int from a set of integers from x to y

Need to find: Probability that Ann's integer is greater than Bob's integer = P(A>B)

Statement 1: y - x = 9
No. of int in the set = y - x + 1 = 9 + 1 = 10

Total no. of possible pairs = 10*10 = 100
No. of pairs where A>B = (9*10)/2 = 45
(A can pick any int other than the lowest one)

Statement 1 is sufficient

Statement 2: y=−20
No information about x
Not Sufficient

Ans. A
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Statement 1:
y-x =9
So, they are 10 consecutive numbers. We don't know what either Ann or Bob will select, so no way to answer.

Statement 2:
y=-20
No information about x. Still can't say what they will select.

Both together:
y-x=9 and y=-20
So, x=-29

Ann and Bob select from [-29,-20]. It still can't be answered.

So, option E.
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So we need to find the probability that the integer Ann selects is greater than the one Bob selects.
(1) y - x = 9.
this gives us a range of numbers, that we can arrange in ascending order.
x, x+1, x+ 2, x+3, ..., x+9.
Now we can find all ways of selection two integers such that one is bigger than the other- (x+1, x)... and so on (our favorable outcomes)
We divide the number of favorable outcomes by total number of outcomes (ways of selecting two integers), and then we get our required probability.
sufficient

(2) y= -20
This is not sufficient, as we just know one end of the range.
Answer = A
Bunuel
Ann and Bob each randomly select an integer from the integers x to y, inclusive. What is the probability that the integer Ann selects is greater than the one Bob selects?

(1) y - x = 9
(2) y = -20


 


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for the GMAT Club Olympics Competition

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We are given that A and B select an integer between X and Y. We are to find the probability that A picks a higher number than B.

Statement 1 - We are given the difference between X and Y. Therefore, we can infer the number of integers in the set. Since the integers will be ordered in a consecutive manner, this statement is enough to find the probability that A picks a higher number than B regardless of what the integers X and Y themselves are. It does not matter if X is 1 and Y is 10 or if X is 2 and Y is 11. The probability will remain the same and can be determined.

Therefore, this statement is sufficient.

Statement 2 - With just the value of Y, we cannot ascertain the probability unless X is known. Therefore, not sufficient.

Therefore, Option A
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Ann and Bob each randomly select an integer from the integers x to y, inclusive. What is the probability that the integer Ann selects is greater than the one Bob selects?

(1) y - x = 9
Y can be 20,10,-20.......
X can be 11,1,29........
Insufficient

(2) y = -20
We don’t know about X
Insufficient

(1)&(2) together
Y=-20 and X-29
(-29,-28,-27,-26,-25,-24,-23,-22,-21,-20)
Sufficient for finding probability

Answer: C
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(1) only: y - x = 9
So there are total 10 integers from x to y. The probably of Ann and Bob selecting the same numbers = 1 x 1/10 = 1/10.
That means the chance that Ann and Bob picking different numbers are 1 - 1/10 = 9/10. Since each person has the same chance of picking a larger number, the probability that the integer Ann selects is greater than the one Bob selects is 9/10 :2 = 9/20

(2) only: y = -20
We can't conclude anything.

Answer: A
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Given: (x,y)-Range of Integers
P(A)>P(b)

1) y-x=9
Any no can be selected, and if we dont have fix answer-so not sufficient

2) y=-20
here also, no fixed answer

combined also we get, x=-11 so range (-11,-20) but no fixed value of answer so Answer is E
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Given the details,

Considering Statement 1, y - x = 9 gives infinite possibilities, therefore Not Sufficient

Considering Statement 2, y = -20 gives incomplete data when considered alone.

Considering Bot Statements 1 & 2 together, we have y = -20 and x - y = 9; There for x = 29

From this it is possible to calculate the probability of Ann choosing an integer greater than Bob.

Therefore, Correct option is Option C
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Form the prompt, I know that two people are picking an integer from a set of consecutive integers ("from x to y"), inclusive, and they can pick the same integer.

Using statement (1):
We are given the range of the set of integers & can find the number of possible integers they can pick from. Consider how:
the number of integers in a set of consecutive integers = Max - Min + 1
= y - x + 1
= 10

Thus, the there are 10 integers to pick from, and we can find the probability of Ann picking a larger integer than Bon by applying the probability formula where:

P(Ann > Bob) = Number of outcomes where Ann's number is bigger than Bob's / the number of total possible outcomes

At this point, I would quickly consider whether I need anymore info to be able to calculate this and once I realise that I don't, I can move on to statement (2) and conclude that statement (1) alone is sufficient.

Using statement (2):
I know the y value but I can't calculate any probabilities without knowing the x value or the range between the two values. Thus, statement (2) alone is NOT sufficient.

Answer: A) Statement one alone is sufficient

To elaborate on statement (1)'s sufficiency:
If Bob picks x (the smallest number), there are 9 ways in which Ann can pick a larger number
If Bob picks x+1 (the 2nd smallest number), there are 8 ways in which Ann can pick a larger number
etc.....
If Bob picks x + 8 (the 2nd largest number, or y-1), there is 1 way in which Ann can pick a larger number.
Because Bob can pick x OR he can pick x+1 etc. we will add all the outcomes (9+8+7+...+1) to get 45 favourable outcomes

Given Bob and Ann can pick the same number, the total number of possible outcomes is 10C1 x 10C1 = 100

Thus, the probability of Ann picking a larger number than Bob is 45/100 = 0.45

The reason we don't need anymore info is that even if y is negative and therefore x is actually the smaller number, the probability is still the same.
Say for example that y = -20 and thus x = -29;
if Bob picks -21 there is 1 way in which Ann can pick a larger number
If Bob picks -22 there are 2 ways in which Ann can pick a larger number
etc.
We are still left with 45 favourable outcomes out of 100 total possible outcomes.
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Bunuel
Ann and Bob each randomly select an integer from the integers x to y, inclusive. What is the probability that the integer Ann selects is greater than the one Bob selects?

(1) y - x = 9
(2) y = -20


 


This question was provided by GMAT Club
for the GMAT Club Olympics Competition

Win over $30,000 in prizes such as Courses, Tests, Private Tutoring, and more

 


If there are N integers we can select a set of two integers in NC2 ways.

Of the sets created, in half of the set, the first number will be smaller than the second number, and in the other half the second number will be smaller than the first number.

Hence, to answer the question we need to know the number of integers that are present in the set.

Statement 1

(1) y - x = 9

Number of integers = y - x + 1 = 10

As we have the number of integers in the set, we can find the probability. As this is DS question we dont' actually need to calculate but knowing the fact that it can be done so is enough.

Statement is sufficient.

Statement 2

(2) y = -20

We cannot determine the number of integers in the set.

Not sufficient.

Option A
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To find probability we need two informations
Number of possible outcomes and total number of outcomes

It is given that Ann can select one integer and Bob can also select one integer, so we need one more information about total number of outcomes to answer this question.

Statement 1:
y-x = 9
We can find out the total number of outcomes = y-x+1 = 10 (when both extreme numbers are mentioned as inclusive)

So this is sufficient to answer the question.
Eliminate B, C and D

Statement 2:
y = -20

We do not have any information about the lower boundary ie x
So we can't calculate total number of outcomes
Hence this statement is insufficient

So option A is correct
Bunuel
Ann and Bob each randomly select an integer from the integers x to y, inclusive. What is the probability that the integer Ann selects is greater than the one Bob selects?

(1) y - x = 9
(2) y = -20


 


This question was provided by GMAT Club
for the GMAT Club Olympics Competition

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