Probability Questions Help (1 Viewer)

[Dash8]

Apparently probability is supposed to be easy but I'm finding it really confusing.....

Would anyone be able to please answer these questions for me with working? They are out of the 'Maths in Focus' text book from 'Tree Diagrams and Probability Trees' in Exercise 11.5.

7. The probability of a certain type of photocopier needing a service on any one day is 0.3. Find the probability that a school with two of these photocopiers will need to service, on a particular day,
(a) 1 machine
(b) Both machines
(c) neither of them

9. A certain type of plant has a probability of 0.85 of producing a variegated leaf. If I grow three of these plants, find the probability of getting a variegated leaf in
(a) two of the plants
(b) none of the plants
(c) at least one plant

11. A bad contains 3 yellow balls, 4 pink balls and 2 black balls. If 2 balls are chosen at random, find the probability of getting a yellow and a black ball
(a) with replacement
(b) without replacement

There's others I'm stuck on but if I manage to understand these hopefully I can do the other ones. Thanks for you help!

 

[barbernator]

Ill just leave them in unsimplified form.
7a) 0.3x0.7x2
b) 0.3x0.3
c) 0.7x0.7
- to check if your correct, all 3 of these answers should sum to 1 because it checks all possibilities of the sample space.
9.a)3C2x0.85x0.15
b)0.15x0.15x0.15
c) 3C1x0.15x0.15x0.85+3C2x0.15x0.85x0.85+3C3x0.85x0.85x0.85
11.a) (3/9)x(2/9)
b) (3/9)x(2/8)+(2/9)(3/8)

hope that helps, they should all be correct. if you have any questions about any of my working just ask

 

[Dash8]

Ill just leave them in unsimplified form.
7a) 0.3x0.7x2
b) 0.3x0.3
c) 0.7x0.7
- to check if your correct, all 3 of these answers should sum to 1 because it checks all possibilities of the sample space.
9.a)3C2x0.85x0.15
b)0.15x0.15x0.15
c) 3C1x0.15x0.15x0.85+3C2x0.15x0.85x0.85+3C3x0.85x0.85x0.85
11.a) (3/9)x(2/9)
b) (3/9)x(2/8)+(2/9)(3/8)

hope that helps, they should all be correct. if you have any questions about any of my working just ask

Hey thanks for you answer

Just one thing, what does the 'C' mean in your calculations?

 

[RealiseNothing]

Hey thanks for you answer

Just one thing, what does the 'C' mean in your calculations?

Combinations.

 

[Dash8]

Combinations.

So I do the same calculation three times?

 

[barbernator]

sorry, it is a term only used in 3u mathematics, umm basically 3C1=3, 3C2=3, 3C3=1.

 

[Dash8]

Ill just leave them in unsimplified form.
7a) 0.3x0.7x2
b) 0.3x0.3
c) 0.7x0.7
- to check if your correct, all 3 of these answers should sum to 1 because it checks all possibilities of the sample space.
9.a)3C2x0.85x0.15
b)0.15x0.15x0.15
c) 3C1x0.15x0.15x0.85+3C2x0.15x0.85x0.85+3C3x0.85x0.85x0.85
11.a) (3/9)x(2/9)
b) (3/9)x(2/8)+(2/9)(3/8)

hope that helps, they should all be correct. if you have any questions about any of my working just ask

hmmm, with question 9 (a), the answer in the book says .325 but I get .383 with your calculations.

For question 11 (a), the book says 4/27 but I get 2/27 with you calculations.

Also, I don't understand Q9 (c) and Q11 (b).

argh why is this so difficult Thanks for your help though

 

[barbernator]

hmmm, with question 9 (a), the answer in the book says .325 but I get .383 with your calculations.

For question 11 (a), the book says 4/27 but I get 2/27 with you calculations.

Also, I don't understand Q9 (c) and Q11 (b).

argh why is this so difficult Thanks for your help though

for 9a, i forgot to put an extra x0.85 in.
for 11a i forgot to put a x2 in.

 

[shamimi95]

hmmm, with question 9 (a), the answer in the book says .325 but I get .383 with your calculations.

For question 11 (a), the book says 4/27 but I get 2/27 with you calculations.

Also, I don't understand Q9 (c) and Q11 (b).

argh why is this so difficult Thanks for your help though

9(b) and 9(c) are complementary events so 1-(0.15)^3 should be your answer