Z is the set of the first n positive odd numbers, where n is a positive integer. Given that n > k, where k is also a positive integer, x is the maximum value of the sum of k distinct members of Z, and y is the minimum value of the sum of k distinct members of Z, what is x + y?
(A) kn
(B) kn + k^2
(C) kn + 2k^2
(D) 2kn - k^2
(E) 2kn
The OA is the option E.
How can I solve this PS question? I'm really confused here.
Experts, can you give me some help?
Z is the set of the first n positive odd numbers, where ....
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Hi Vincen,Z is the set of the first n positive odd numbers, where n is a positive integer. Given that n > k, where k is also a positive integer, x is the maximum value of the sum of k distinct members of Z, and y is the minimum value of the sum of k distinct members of Z, what is x + y?
(A) kn
(B) kn + k^2
(C) kn + 2k^2
(D) 2kn - k^2
(E) 2kn
The OA is the option E.
How can I solve this PS question? I'm really confused here.
Experts, can you give me some help?
Let's take a look at your question.
We will solve this question by assuming some random values for the set Z.
Let n = 5, therefore, the set Z has first 5 positive odd numbers. i.e.
$$Z=\left\{1,\ 3,\ 5,\ 7,\ 9\right\}$$
Let k = 2,
then x is the is the maximum value of the sum of k=2 distinct members of Z.
We can see that the two values of set Z, that will give the maximum sum are the last two values, i.e. 7 and 9. Therefore,
$$x=7+9=16$$
y is the is the minimum value of the sum of k=2 distinct members of Z.
We can see that the two values of set Z, that will give the minimum sum are the first two values, i.e. 1 and 3. Therefore,
$$y=1+3=4$$
Now, we can find x+y:
$$x+y=16+4=20$$
We had: n = 5 and k = 2
So 20 will be equal to:
$$2\times5\times2=2nk$$
Therefore, option E is correct.
Hope it helps.
I am available if you'd like any follow up.
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We can let n = 5 and k = 3. Thus Z = {1, 3, 5, 7, 9}, x = 5 + 7 + 9 = 21, y = 1 + 3 + 5 = 9 and hence x + y = 21 + 9 = 30.Vincen wrote:Z is the set of the first n positive odd numbers, where n is a positive integer. Given that n > k, where k is also a positive integer, x is the maximum value of the sum of k distinct members of Z, and y is the minimum value of the sum of k distinct members of Z, what is x + y?
(A) kn
(B) kn + k^2
(C) kn + 2k^2
(D) 2kn - k^2
(E) 2kn
The OA is the option E.
How can I solve this PS question? I'm really confused here.
Experts, can you give me some help?
Now let's check the given answer choices (note: we will be looking for the one that is equal to 30):
A) kn = 5(3) = 15 → This is not 30.
B) kn + k^2 = 5(3) + 3^2 = 15 + 9 = 24 → This is not 30.
C) kn + 2k^2 = 5(3) + 2(3)^2 = 15 + 18 = 33 → This is not 30.
D) 2kn - k^2 = 2(5)(3) - 3^2 = 30 - 9 = 21 → This is not 30.
E) 2kn = 2(5)(3) = 30 → This is 30
Answer: E
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