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If set A={a,b,c,d,e}, what is the number of subsets that must include

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If set A={a,b,c,d,e}, what is the number of subsets that must include  [#permalink]

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New post 27 Jun 2017, 01:05
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If set A={a,b,c,d,e}, what is the number of subsets that must include only 3 elements?

A. 8
B. 10
C. 12
D. 15
E. 18

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Re: If set A={a,b,c,d,e}, what is the number of subsets that must include  [#permalink]

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New post 27 Jun 2017, 01:06
Chosing 3 elements out of 5 : 5c3 = 10 = B
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If set A={a,b,c,d,e}, what is the number of subsets that must include  [#permalink]

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New post 27 Jun 2017, 01:21
MathRevolution wrote:
If set A={a,b,c,d,e}, what is the number of subsets that must include only 3 elements?

A. 8
B. 10
C. 12
D. 15
E. 18


Set A={a,b,c,d,e}

Number of ways to select 3 elements from set of 5 elements \(= \frac{5!}{3!(5-3)!}\)

\(\frac{5!}{3!2!} = \frac{5 * 4* 3*2}{3*2 * 2} = 5 * 2 = 10\). Answer (B)...


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If set A={a,b,c,d,e}, what is the number of subsets that must include  [#permalink]

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New post 27 Jun 2017, 05:47
Question asks how many ways can you choose 3 items out of 5 = 5C3 = 10
Answer B
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New post 29 Jun 2017, 02:59
==> You get 5C3=5C2=(5)(4)/2!=10.

The answer is b.
Answer: B
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Re: If set A={a,b,c,d,e}, what is the number of subsets that must include  [#permalink]

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New post 29 Jun 2017, 15:19
If set A={a,b,c,d,e}, what is the number of subsets that must include only 3 elements?

\(= 5C2\)

\(= \frac{5!}{2! * 3!}\)

\(= 5 * 2\)

\(= 10\)

Hence, Answer is B
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Re: If set A={a,b,c,d,e}, what is the number of subsets that must include   [#permalink] 29 Jun 2017, 15:19
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