huda wrote:
chid2 wrote:
7 people :
1 siblings : A A ; B B
2 siblings : C C C
Probability not siblings
Case A (selecting A; and non siblings) : 2/7 x 5/6 = 10/42
Case B (selecting B; and non siblings ) : 2/7 x 5/6 = 10/42
Case C (selecting C; non siblings ) : 3/7 x 4/6 = 12/42
Adding all and we have answer E
What, if we selected
1 sibling: A B ; C D
2 siblings: X Y Z
Than what,s happed to the Probability not siblings, and then the answer?
Sure we can, but it will be very confusing
Let us assume, those 7 people are A, B, C, D, X, Y and Z
A have B and C as siblings
B - A and C
C- A and B
D - X
X - D
Y - Z
Z - Y
So 4 of them have 1 sibling and 3 have 2 siblings
Total cases = 7C2 = 21
favorable cases =16 (AD, AX, AY, AZ, BD, BX, BY, BZ, CD, CX, CY, CZ, DY, DZ, XY and XZ)
So. 16/21
Option E