7. A bag contains $n$ red balls, $n$ yellow balls, and $n$ blue balls. One ball is selected at random and not replaced. A second ball is then selected at random and not replaced. Each ball is equally likely to be chosen. The probability that the two balls are not the same colour is A $\frac { n - 1 } { 3 n - 1 }$ B $\frac { 2 n - 2 } { 3 n - 1 }$ C $\frac { 2 n } { 3 n - 1 }$ D $\quad \frac { ( n - 1 ) ^ { 3 } } { 27 ( 3 n - 1 ) ^ { 3 } }$ E $\quad \frac { 3 ( n - 1 ) } { 3 n - 1 }$ F $\quad \frac { n ^ { 3 } } { 27 ( 3 n - 1 ) ^ { 3 } }$
7. A bag contains $n$ red balls, $n$ yellow balls, and $n$ blue balls.
One ball is selected at random and not replaced.\\
A second ball is then selected at random and not replaced.\\
Each ball is equally likely to be chosen.\\
The probability that the two balls are not the same colour is
A $\frac { n - 1 } { 3 n - 1 }$\\
B $\frac { 2 n - 2 } { 3 n - 1 }$\\
C $\frac { 2 n } { 3 n - 1 }$\\
D $\quad \frac { ( n - 1 ) ^ { 3 } } { 27 ( 3 n - 1 ) ^ { 3 } }$\\
E $\quad \frac { 3 ( n - 1 ) } { 3 n - 1 }$\\
F $\quad \frac { n ^ { 3 } } { 27 ( 3 n - 1 ) ^ { 3 } }$\\