Probaility - help needed ASAP (1 Viewer)

[Petinga]

1. Two spinners are spun simultaneously. First spinner has the numbers 1,2,3 and each of these numbers are equally likely. The 2nd spinner has the numbers 1,3,5,7 and each of the outomes are equally likely.
a)what is the probabilty that both spinners stop on the same number?
b)what is the probabilty that at least one of the spinners stops on 3?

2. Chris has 4 pairs of socks in a drawer, each pair a differetn colour. He selects socks one at a time and at random from the drawer.
a) The probability that he does NOT have a matchjing pair after selecting the second sock is 6/7. Explain why this is so.
b)Find the probabilty that he does NOT have a matching pair after selecting the third sock.
c) What is the probability that the first three socks include a matching pair?

3. In a game, a turn invloves rolling two dice, each with faces marked 0,1,2,3,4 and 5. The score for each turn is calculated by multiplying the two numbers uppermost on the dice.
c)what is the probability that the sum of the scores in the first two turns is less than 45?

 

[webby234]

1a) 1/3 * 1/4+ 1/3 * 1/4

= 1/6

b) 1 - (2/3 * 3/4)

= 1/2

 

[webby234]

2a) After one sock is picked out there are seven socks left in the drawer, one of which is the same as the one already drawn. Therefore the probability of the second sock being the same as the first is 1/7.

b) 6/7 * 4/6 (two different socks will give a pair in the third draw)

= 4/7

c) 1 - 4/7 = 3/7

 

[webby234]

3) Ways of getting 45 or more

(4,5) + (5,5)
(5,4) + (5,5)
(5,5) + (4,5)
(5,5) + (5,4)
(5,5) + (5,5)

Total no. possibilities = 1/36 * 1/36 = 1/1296

so P of getting 45 or more = 5/1296

so P getting less than 45 = 1291/1296