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first statement mentions that y - x = 9, which means that y = x+9. If both inclusive, that means 10 consecutive digits.

In 10 consecutive digits, there are a total number of 100 pair combinations. Among those 100 hundred, lets assume we need to consider only the cases where the first number of the pair is greater than the second number. Below are the cases when the first number is:
Smallest number = 0 smaller numbers, hence 0 pairs possible
2nd smallest number = 1 smaller number, 1 pair possible
3rd smallest number = 2 smaller numbers, 2 pairs possible
.
.
.
Largest number = 9 smaller numbers, 9 pairs possible.

Adding it all up = 1+2+3+....+9 = 9*10/2 = 45 possible cases where Ann's number is greater than Bob's. Hence the probability would be 45/100 = 0.45, which means statement 1 is sufficient.

The second statement mentions that y = -20. Since we are not sure what x is, we can't definitely find the probability, so statement 2 is not sufficient.

Answer = A
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The first statement secure that integers are different, thus we can say the chances are 50%. The second only give us information about one number, the integer x could be -20 too, more or less than it.
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Just knowing the number of options they have will allow us to calculate the probability. We only need to calculate the probability of them choosing the same number, then the rest is equal between either Ann choosing the bigger number or Ben choosing the bigger number.

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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IMO should be A

We just need to know the total number of integers to understand the probablity. The formula is P(Ann is greater)+P(Bob is greater)+P(both are equal)=1. But we know that the probablity of ann getting a greater number is the same as bob getting a greater number. So the formula becomes:

2*P(Ann is greater)+P(both are equal)=1

If we now know the total number of integers, we can easily calculate the probablities. Only option A gives us that.
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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Out of a set of \(n\) integers, \(a \text{ & } b\) can be selected in \(nP2\) ways. In this, half pairs will be where \(a>b\) & the remaining half will be where \(a<b\)

Als0, there will be \(n\) pairs where \(a=b\)

So, the probability of \(a>b = \frac{nP2}{2*(nP2+n)}\)

if n is the only unknown

Statement 1: \(y - x = 9\)

\(y=x+9\)

So there are 10 integers in the set \(a \text{ & } b\) inclusive.

\(n=10\)

Sufficient

Statement 2: \(y = -20\)

The value of \(y\) alone is not enough for a solution

Not Sufficient

Answer: A
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To calculate the probability, we must have the information about the values of x and y. Statement (1) only provides information about the range between x and y. Statement (2) provides the value of y but not x. When considering both statements together, we can solve for the value of x and thus have enough inputs to calculate the probability
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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If there are n integers, the total outcomes are n * n = n^2.
If the integers are from x to y inclusive, and there are n = y - x + 1 integers.

For Ann's number to be greater than Bob's:
- If Bob selects the smallest number (x), Ann can select any of the n - 1 larger numbers.
- If Bob selects the next number (x + 1), Ann can select any of the n - 2 larger numbers.
...
- If Bob selects the largest number (y), Ann cannot select a larger number (0 possibilities).

So total favorable outcomes = (n - 1) + (n - 2) + ... + 1 + 0 = n(n - 1)/2
The probability P(Ann > Bob) = [n(n - 1)/2] / n^2 = (n - 1)/2n.

(1) y - x = 9
The number of integers is n = y - x + 1 = 10.
P(Ann > Bob) = (10 - 1)/(2*10) = 9/20.

Statement (1) alone is sufficient.

(2) y = -20
This tells us y is -20, but we don't know x, so we don't know the range. Without knowing x, we can't determine n, and thus can't find the probability.

Statement (2) alone is insufficient.

Answer A
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Since Ann’s probability of picking a larger number depends only on the size of the interval (n = y–x+1) via P = (y–x)/[2(y–x+1)], knowing y–x = 9 (so n = 10) gives P = 9/20, which pins it down uniquely statement (1) is sufficient. Knowing only y = –20 leaves x (and thus the interval size) undetermined, so statement (2) is not sufficient. Therefore, (1) alone suffice

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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Ans: A
1)
y-x=9
the probability Ann> Bob is 9/20 hence, suffi
2)
no info. about x (insuffi)
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From the options only the range of X-Y is determined and not the probability of choosing the number.
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It's not possible to know the prob.
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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Ann and Bob are picking from the same set of integers:

{x,x+1,...,y}

Statement 1: y-x=9.

The total number of integers= y−x+1= 9+1=10.

Since both pick randomly and independently, and from the same set, the p(A) > p(B) depends on how many of such ordered pairs exist.

Total number of possible pairs
(a,b)=10×10=100

For a fixed set of 10 integers, the number of pairs where A>B is always the same:

Number of A>B outcomes=
10(10−1)/2 = 45
Total outcomes = 100

P(A>B)= 45/100= 0.45.

Statement (1) is sufficient.

Statement (2):

y=−20
The size of the set is unknown.

For ex:

If x=−29, then there are 10 integers
If x=−24, then there are 5 integers

The probability depends on the size of the set. So the set could vary in size,
P(A>B) will also vary.

Statement (2) is not sufficient.

Statement 1 alone is sufficient, but statement 2 alone is not sufficient.

Answer - A.
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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
1) y−x=9
There are 10 integers in the range.
Total pairs = 100.
Equal pairs = 10 (diagonal).
Ann > Bob in 45 cases.
So, P=45/100=9/20
Sufficient

(2) y=−20
We don’t know x, so the range size is unknown.
Probability depends on how many integers are in the range
Not sufficient

A
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For any two distinct selections (where Ann /= Bob), exactly half the time Ann will be greater than Bob (since the selections are symmetric). The probability they select the same number is 1/n (since there are n numbers).

Ann > Bob: P = [1 - P(Ann = Bob)] / 2 = (1 - 1/n)/2 = (n - 1)/(2n).

(1)
n=10
P=9/20

Sufficient

(2)
We don't know the range.

Insufficient

Correct answer is A
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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

 

From statement 1 it is clear that two numbers have a difference of 9 which means we can have any number (for Ann and Bob we can select from these 10 umbers) which can be like
10,1 or 100,110 .... similallry so we can have 100 such arrangements for Ann and Bob and we have to find how many of them is such that Ann has more than Bob.

So in 100 numbers we can have only 45 ways so one number is greater than other (excluding situations when both are same) so 45/100 is the probability. which makes A sufficient.


Now, 2 cannot be solution since if y is a fixed value, their can be inffinite numbers x which is greater so we cannot find probbaility
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Statement 1: y−x=9y - x = 9y−x=9

That means there are 10 numbers total (from xxx to yyy)
So there are 10×10=10010 \times 10 = 10010×10=100 total possible outcomes.
Of those, 45 are cases where Ann > Bob (it’s a known pattern).

So:
Probability=45100=0.45\text{Probability} = \frac{45}{100} = 0.45Probability=10045=0.45
Sufficient – we can calculate the exact probability.

Statement 2: y=−20y = -20y=−20
We don’t know xxx, so we don’t know how many numbers are in the range.
Could be:
  • 10 numbers → same probability as before
  • Or 5 numbers → totally different result
Not sufficient

Final Answer:(A) – Only Statement 1 is sufficient.
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Statement (1): Tells us y−x=9, so there are 10 integers in the range. With a fixed number of values, we can compute the exact probability that Ann’s number is greater than Bob’s. Sufficient.

Statement (2): Gives only y=−20, but without knowing
x, we don’t know how many integers are in the range—so we can’t determine the probability. Not sufficient.

Ans: A
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