perm/comb quest. from camb(3u) (1 Viewer)

[Rahul]

this question is from ex 10F.

13 a) how many 5-letter words can b formedd by using the letters of the word STRESS?

14 6-letter words are formed using two A's and four B's. By referrring to the relevant section of the notes, show how all teh differnent possiblilities of words can be derived from the expansion of (A+B)^6. -an explanation will prolly do-

thanks.

 

[Constip8edSkunk]

a)
with 2S: 5!/2!=60
with 3S: 3*5!/3!=60
add the 2, total number of words = 120

b) think about applyin the binomial thrm... where each coefficient represent a differetn number of letters and work from there.

 

[...]

Originally posted by Constip8edSkunk
a)
with 2S: 5!/2!=60
with 3S: 3*5!/3!=60
add the 2, total number of words = 120

so then ur only assuming that from that 5 letters...u can only make the word STRESS???

 

[Rahul]

constipated, i got it thanks. there are only two possible combinations, with 2S's or 3S's.