Class 11

Math

Algebra

Permutations and Combinations

A meeting is to be addressed by 5 speakers A, B, C, D, E. In how many ways can the speakers be ordered, if B must not precede A (immediately or otherwise)?

- $120$
- $24$
- $60$
- $5_{4}×4$

Meeting is to be addressed by $5$ speakers $a,b,c,d,e$

$5$ speaker can be address in $5!$ ways $=120$

Either $b$ can speak before a or after a

ways the speaker be ordered is $b$ must not precede $a=2120 =60$

$∴$ Answer is $60$ ways