3 people have exactly 2 siblings. This means three of them are siblings.
4 people have exactly one sibling.
Total no of ways of selecting 2 people from 7 = 7C2 = 21
No of ways favorable ways.
1. If we select One from the group of 3(2 siblings) and one from the group of 4(1 sibling) = 3C1*4C1 = 12
2. If we select 2 from the group of 4 who are not siblings = 4C2( Total Selections) - 2 ( Selections with siblings) = 4
Probability = 16/21.
Thanks
raama
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siblings
Source: Beat The GMAT — Problem Solving |
thanks!
but i still can't understand the second step in solving a problem. can you please elaborate on that part?
but i still can't understand the second step in solving a problem. can you please elaborate on that part?
Four of them has exactly one siblingFeruza Matyakubova wrote:thanks!
but i still can't understand the second step in solving a problem. can you please elaborate on that part?
a,b,c,d are the members of the group.
Assume that a,b and c,d are siblings.
2 people from 4 will be selected in 4C2 = 6 ways.
These 6 ways include selecting (a,b) and (c,d). We have to exclude them.
So 6 -2 = 4 ways we can select 2 people who are not sibllings.
Thanks
Raama
No of ways favorable ways.
1. If we select One from the group of 3(2 siblings) and one from the group of 4(1 sibling) = 3C1*4C1 = 12
2. If we select 2 from the group of 4 who are not siblings = 4C2( Total Selections) - 2 ( Selections with siblings) = 4
Question: In this why are we not considering 2 from group of 3 men who are not siblings??
1. If we select One from the group of 3(2 siblings) and one from the group of 4(1 sibling) = 3C1*4C1 = 12
2. If we select 2 from the group of 4 who are not siblings = 4C2( Total Selections) - 2 ( Selections with siblings) = 4
Question: In this why are we not considering 2 from group of 3 men who are not siblings??
Each one from that group has 2 siblings.Tryingmybest wrote:No of ways favorable ways.
1. If we select One from the group of 3(2 siblings) and one from the group of 4(1 sibling) = 3C1*4C1 = 12
2. If we select 2 from the group of 4 who are not siblings = 4C2( Total Selections) - 2 ( Selections with siblings) = 4
Question: In this why are we not considering 2 from group of 3 men who are not siblings??
Like A has B and C as siblings.
B has A and C as siblings.
C has A and B as siblings.
Thanks
Raama
Here is my Vision of it
A-B C- D X- Y-Z
- denotes siblings
Selecting 2 from 7 = 7 C2 = 21
Pairs which are not siblings = AC ,AD,AX,AY,AZ,BC,BD,BX,BY,BZ,CX,CY,CZ,DX,DY,DZ
So Probability = 16/21
Thanks
A-B C- D X- Y-Z
- denotes siblings
Selecting 2 from 7 = 7 C2 = 21
Pairs which are not siblings = AC ,AD,AX,AY,AZ,BC,BD,BX,BY,BZ,CX,CY,CZ,DX,DY,DZ
So Probability = 16/21
Thanks
