Gen Math Help - Probability!! HELP (1 Viewer)

[Chrissiee]

I suck at probability and these questions are annoying me so bad! I see how you get the answer to some of them but i can't find the reasoning... can anyone explain any of these to me?

1. There are five women and six men in a group. From this group a committee of 4 is to be chosen. How many different ways can a committee be formed that contain at least three women?
Answer: 65

2. A man hit a target once in 4 shots. If he fires 4 shots in succession, what is the probability that he will hit his target?
Answer: 175/265

3. In how many ways can 5 letters be posted in 3 post boxes, if any number of letters can be posted in all of the three post boxes?
Answer: 3^5 (3 to the power of 5)

4. 10 coins are tossed simultaneously. In how many of the outcomes will the third coin turn up a head?
Answer: 2^9 (2 to the power of 9)

5. Anthony and Michael sit on the six member board of directors for company X. If the board is to be split up into 2 three-person subcommittees, what percent of all the possible subcommittees that include Michael also include Anthony?
Answer: 20%


Thank you!!!

p.s. will rep if you can explain it

 

[SpreadTheWord]

Are you sure the first one isn't 66?

I did 5P3 + 6P1 = 66. Nothing else gets close.

 

[Chrissiee]

Are you sure the first one isn't 66?

I did 5P3 + 6P1 = 66. Nothing else gets close.

no the answer to 1 is:
5C3 x 6C1 + 5C4 x 6C0
= 10x6 +5x1
= 60 + 5
= 65

I figured that one out. What confused me at the beginning was why do you times but then i go it.
Can anyone do any of the others and explain why?

 

[Jaymay]

Well 2...

If he hits... Than it P(1-Missing all)

If the chance of missing is 3/4, and its succession of 4...

(3/4)^4 = 81/256

1-Ans = 175/256

 

[Chrissiee]

Well 2...

If he hits... Than it P(1-Missing all)

If the chance of missing is 3/4, and its succession of 4...

(3/4)^4 = 81/256

1-Ans = 175/256

I still don't get it. Can you explain why the probability is p(1-missing all)?

 

[dannnys]

basically Jays saying for 2:
1 = missing + not missing
therefore, he's caculated that missing is (3/5)^4 which = 81/256
so therefore the probability of hitting is: 1-missing = 1 - 81/256
therefore the probability of hitting is 175/256
i hope i havent complicated it lol... =/