Evaluate the expression.
-${ } _ { 9 } \mathrm { C } _ { 2 }$
A) 181440
B) 72
C) $\frac { 9 } { 14 }$
D) 36

Question

Quizplus · Accepted Answer

${ } _ { 9 } \mathrm { C } _ { 2 }$ calculates the number of combinations of 9 items taken 2 at a time. The formula for combinations is ${ } _ { n } \mathrm { C } _ { r } = \frac{n!}{r!(n-r)!}$. Plugging in 9 for $n$ and 2 for $r$, we get $\frac{9!}{2!(9-2)!} = \frac{9 \times 8}{2} = 36$.

Evaluate the Expression 9C2{ } _ { 9 } \mathrm { C } _ { 2 }9​C2​

Evaluate the Expression ${ } _ { 9 } \mathrm { C } _ { 2 }$