A-Level Maths OCR B (MEI) (H640)

Know the notations $n!$ and $_nC_r$ and that $_nC_r$ is the number of ways of selecting $r$ distinct objects from $n$.

The meaning of the term factorial.

$n$ a positive integer.

Link to binomial probabilities.

Notation:

• $_nC_r = \dfrac{n!}{r!(n-r)!}$
• $n! = 1×2×3×...×n$
• $_nC_0 = _nC_n = 1$
• $0! = 1$
• $^nC_r, \dbinom{n}{r}$

Excludes: $_nC_r$ will only be used in the context of binomial expansions and binomial probabilities.