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The subsets of the set {s, t, u} consisting of the three elements s, t
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Updated on: 09 Jan 2019, 02:51

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The subsets of the set {s, t, u} consisting of the three elements s, t, and u are {s}, {t}, {u}, {s, t}, {s, u}, {t, u}, {s, t, u}, and the empty set { }. How many different subsets of the set {s, t, u, w, x} do not contain t as an element?

Re: The subsets of the set {s, t, u} consisting of the three elements s, t
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27 Nov 2012, 02:02

saxenarahul021 wrote:

The subsets of the set {s, t, u} consisting of the three elements s, t, and u are {s}, {t}, {u}, {s, t}, {s, u}, {t, u}, {s, t, u}, and the empty set { }. How many different subsets of the set {s, t, u, w, x} do not contain t as an element?

A. 4 B. 7 C. 8 D. 15 E. 16

Consider the set without t: {s, u, w, x}. Each subset of this set will be subset of the original set but without t.

# of subsets of {s, u, w, x} is 2^4=16 (each out of 4 element of the set {s, u, w, x} has TWO options: either to be included in the subset or not, so total # of subsets is 2^4=16).

Re: The subsets of the set {s, t, u} consisting of the three elements s, t
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29 Nov 2012, 00:52

Bunuel wrote:

saxenarahul021 wrote:

The subsets of the set {s, t, u} consisting of the three elements s, t, and u are {s}, {t}, {u}, {s, t}, {s, u}, {t, u}, {s, t, u}, and the empty set { }. How many different subsets of the set {s, t, u, w, x} do not contain t as an element?

A. 4 B. 7 C. 8 D. 15 E. 16

Consider the set without t: {s, u, w, x}. Each subset of this set will be subset of the original set but without t.

# of subsets of {s, u, w, x} is 2^4=16 (each out of 4 element of the set {s, u, w, x} has TWO options: either to be included in the subset or not, so total # of subsets is 2^4=16).

Answer: E.

I am a little bit confused by your solution can you please clarify. I agree we need to find out how many subsets are possible without t, so 4 letter could have 1 set ({SUWX} 4!/4!=1), 3 letters could have 4 sets (4!/3!=4), 2 letters could have 6 sets (4!/2!x2!=6), and 1 letter could have 4 sets. So overall 15 sets and the answer is D. Where did i go wrong?
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Re: The subsets of the set {s, t, u} consisting of the three elements s, t
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29 Nov 2012, 01:59

ziko wrote:

Bunuel wrote:

saxenarahul021 wrote:

The subsets of the set {s, t, u} consisting of the three elements s, t, and u are {s}, {t}, {u}, {s, t}, {s, u}, {t, u}, {s, t, u}, and the empty set { }. How many different subsets of the set {s, t, u, w, x} do not contain t as an element?

A. 4 B. 7 C. 8 D. 15 E. 16

Consider the set without t: {s, u, w, x}. Each subset of this set will be subset of the original set but without t.

# of subsets of {s, u, w, x} is 2^4=16 (each out of 4 element of the set {s, u, w, x} has TWO options: either to be included in the subset or not, so total # of subsets is 2^4=16).

Answer: E.

I am a little bit confused by your solution can you please clarify. I agree we need to find out how many subsets are possible without t, so 4 letter could have 1 set ({SUWX} 4!/4!=1), 3 letters could have 4 sets (4!/3!=4), 2 letters could have 6 sets (4!/2!x2!=6), and 1 letter could have 4 sets. So overall 15 sets and the answer is D. Where did i go wrong?

You are forgetting an empty set, which is also a subset of {s, u, w, x} and do not contain t.
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Re: The subsets of the set {s, t, u} consisting of the three elements s, t
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29 Nov 2012, 04:58

I am a little bit confused by your solution can you please clarify. I agree we need to find out how many subsets are possible without t, so 4 letter could have 1 set ({SUWX} 4!/4!=1), 3 letters could have 4 sets (4!/3!=4), 2 letters could have 6 sets (4!/2!x2!=6), and 1 letter could have 4 sets. So overall 15 sets and the answer is D. Where did i go wrong?[/quote]

You are forgetting an empty set, which is also a subset of {s, u, w, x} and do not contain t.[/quote]

Thanks Bunuel, i got it, but do you think the way of thinking was correct?
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Re: The subsets of the set {s, t, u} consisting of the three elements s, t
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29 Nov 2012, 07:27

ziko wrote:

Thanks Bunuel, i got it, but do you think the way of thinking was correct?

Yes, your approach is correct: # of subsets with 4 elements is 1: \(C^4_4=1\); # of subsets with 3 elements is 4: \(C^3_4=4\); # of subsets with 2 elements is 6: \(C^2_4=6\); # of subsets with 1 elements is 4: \(C^1_4=4\); plus 1 empty set.

Re: The subsets of the set {s, t, u} consisting of the three elements s, t
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12 May 2014, 13:22

saxenarahul021 wrote:

The subsets of the set {s, t, u} consisting of the three elements s, t, and u are {s}, {t}, {u}, {s, t}, {s, u}, {t, u}, {s, t, u}, and the empty set { }. How many different subsets of the set {s, t, u, w, x} do not contain t as an element?

A. 4 B. 7 C. 8 D. 15 E. 16

I thought that the formula for number of subsets for n elements was 2^n -1

Can anybody explain why this formula does not apply in this case?

Re: The subsets of the set {s, t, u} consisting of the three elements s, t
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13 May 2014, 00:03

jlgdr wrote:

saxenarahul021 wrote:

The subsets of the set {s, t, u} consisting of the three elements s, t, and u are {s}, {t}, {u}, {s, t}, {s, u}, {t, u}, {s, t, u}, and the empty set { }. How many different subsets of the set {s, t, u, w, x} do not contain t as an element?

A. 4 B. 7 C. 8 D. 15 E. 16

I thought that the formula for number of subsets for n elements was 2^n -1

Can anybody explain why this formula does not apply in this case?

Thanks! Cheers J

The number of subsets of a set with n elements is 2^n, including an empty set.
_________________

Re: The subsets of the set {s, t, u} consisting of the three elements s, t
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06 Dec 2018, 16:16

Top Contributor

saxenarahul021 wrote:

The subsets of the set {s, t, u} consisting of the three elements s, t, and u are {s}, {t}, {u}, {s, t}, {s, u}, {t, u}, {s, t, u}, and the empty set { }. How many different subsets of the set {s, t, u, w, x} do not contain t as an element?

A. 4 B. 7 C. 8 D. 15 E. 16

Take the task of building subsets and break it into stages.

Stage 1: Determine whether or not to place "t" in the subset The question tells us that "t" cannot be in the subset. So, we can complete stage 1 in 1 way (that is, we DO NOT place "t" in the subset

Stage 2: Determine whether or not to place "s" in the subset We can either HAVE "s" in the subset or NOT HAVE "s" in the subset So, we can complete stage 2 in 2 ways

Stage 3: Determine whether or not to place "u" in the subset We can either HAVE "u" in the subset or NOT HAVE "u" in the subset So, we can complete this stage in 2 ways

Stage 4: Determine whether or not to place "w" in the subset We can either HAVE "w" in the subset or NOT HAVE "w" in the subset So, we can complete this stage in 2 ways

Stage 5: Determine whether or not to place "x" in the subset We can complete this stage in 2 ways

By the Fundamental Counting Principle (FCP), we can complete the 5 stages (and thus build all possible subsets) in (1)(2)(2)(2)(2) ways (= 16 ways)

Answer: E

Note: the FCP can be used to solve the MAJORITY of counting questions on the GMAT. So, be sure to learn it.

Re: The subsets of the set {s, t, u} consisting of the three elements s, t
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09 Jan 2019, 02:48

1

saxenarahul021 wrote:

The subsets of the set {s, t, u} consisting of the three elements s, t, and u are {s}, {t}, {u}, {s, t}, {s, u}, {t, u}, {s, t, u}, and the empty set { }. How many different subsets of the set {s, t, u, w, x} do not contain t as an element?

A. 4 B. 7 C. 8 D. 15 E. 16

Dear Moderator, Can we please update the OA for this question, Thank you.
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Re: The subsets of the set {s, t, u} consisting of the three elements s, t
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09 Jan 2019, 02:52

stne wrote:

saxenarahul021 wrote:

The subsets of the set {s, t, u} consisting of the three elements s, t, and u are {s}, {t}, {u}, {s, t}, {s, u}, {t, u}, {s, t, u}, and the empty set { }. How many different subsets of the set {s, t, u, w, x} do not contain t as an element?

A. 4 B. 7 C. 8 D. 15 E. 16

Dear Moderator, Can we please update the OA for this question, Thank you.