pre-permutation/combination help?? (1 Viewer)

[lookoutastroboy]

this question from mathscape yr 10 extension to me looks like a combination/permutation question, and could someone clarify if it is or not and help me with it? i mean in yr 10 are we supposed to know these perms and combs already?

Basheer studies four subjects each semester for six semesters. There are 5 possible results for each subject and the chance of earning each result:
HD: 7%
D: 34%
C: 40%
P: 16%
F: 3%

Q. What is the probability (to nearest 0.1%) of earning no credits in a year (assume this means the total of 24 subjects).
Q. Basheer's friend Simon earns four passes in one semester. What is BASHEER'S LIKELIHOOD (TO NEAREST 0.1%) OF NOT FAILING ANY SUBJECT AND DOING BETTER THAN simon?

I tried a tree diagram for both and it seemed to work but the number of events was in the thousands if im correct. Is there any way to solve these questions otherwise (im not sure if product rule works here btw)






thanks in advance, lookoutastroboy

 

[Timothy.Siu]

umm 24 subjects? P(no credits) is 1-P(all credits)=1-(4/10)²⁴=0.999999999

 

[lookoutastroboy]

oy tim, so these questions have nothin to do with perms/combs (plz tell me they dont =))

 

[Timothy.Siu]

oy tim, so these questions have nothin to do with perms/combs (plz tell me they dont =))

dont think so...

edit: not really sure is it (97/100)⁴-(16/100)⁴

 

[lookoutastroboy]

thanks for the responses - the answers btw for Q1 is 1.7% and Q2. is 88.5%

 

[bored of sc]

Only 2 semesters make up a year, so there are 8 subjects:

i.e. not credit = 1 -credit = 1 -0.4 = 0.6
(0.6)⁸ = 0.01679616 = 1.7%

 

[bored of sc]

(97/100)⁴-(16/100)⁴ = 0.88463745 = 88.5%

That's the answer. Good work.

 

[lookoutastroboy]

ty bored of sc for ur solution, soz for my lack of knowledge on semesters, just one question, is the SC hard??

 

[Timothy.Siu]

ty bored of sc for ur solution, soz for my lack of knowledge on semesters, just one question, is the SC hard??

depends whos doing it. lol, dont stress too much, its not that important if you dont do well, but try your best =)

 

[shaon0]

ty bored of sc for ur solution, soz for my lack of knowledge on semesters, just one question, is the SC hard??

SC is pointless. The best advice is, Don't study!!