a) Let W denote a win, L denote a loss, and D denote a draw.
Given probabilities for a single match:
P(W)=0.6
P(L)=0.3
P(D)=0.1
The team plays two matches. Here is the tree diagram:
Match 1
- Start with a single point.
- Branch 1: Win (W) with probability 0.6
- Branch 2: Lose (L) with probability 0.3
- Branch 3: Draw (D) with probability 0.1
Match 2
- From each outcome of Match 1, draw three new branches for Match 2:
- If Match 1 was W:
- Win (W) with probability 0.6 (Path: WW)
- Lose (L) with probability 0.3 (Path: WL)
- Draw (D) with probability 0.1 (Path: WD)
- If Match 1 was L:
- Win (W) with probability 0.6 (Path: LW)
- Lose (L) with probability 0.3 (Path: LL)
- Draw (D) with probability 0.1 (Path: LD)
- If Match 1 was D:
- Win (W) with probability 0.6 (Path: DW)
- Lose (L) with probability 0.3 (Path: DL)
- Draw (D) with probability 0.1 (Path: DD)
The possible outcomes and their probabilities are:
- P(WW)=0.6×0.6=0.36
- P(WL)=0.6×0.3=0.18
- P(WD)=0.6×0.1=0.06
- P(LW)=0.3×0.6=0.18
- P(LL)=0.3×0.3=0.09
- P(LD)=0.3×0.1=0.03
- P(DW)=0.1×0.6=0.06
- P(DL)=0.1×0.3=0.03
- P(DD)=0.1×0.1=0.01
b) What is the probability that the team will:
i) Win the two matches
This corresponds to the outcome WW.
P(Wintwomatches)=P(W)×P(W)=0.6×0.6=0.36
The probability of winning two matches is 0.36.
ii) Either wins all the matches or loses all the matches
This means the outcomes WW or LL. These are mutually exclusive events.
P(Winsallorlosesall)=P(WW)+P(LL)
P(WW)=0.6×0.6=0.36
P(LL)=0.3×0.3=0.09
P(Winsallorlosesall)=0.36+0.09=0.45
The probability of either winning all matches or losing all matches is 0.45.
iii) Wins one match and loses one
This means the outcomes WL or LW. These are mutually exclusive events.
P(Winsoneandlosesone)=P(WL)+P(LW)
P(WL)=P(Winmatch1)×P(Linmatch2)=0.6×0.3=0.18
P(LW)=P(Linmatch1)×P(Winmatch2)=0.3×0.6=0.18
P(Winsoneandlosesone)=0.18+0.18=0.36
The probability of winning one match and losing one is 0.36.
iv) Tie in one match
This means exactly one match is a draw. The other match must not be a draw.
Let P(notD)=P(W)+P(L)=0.6+0.3=0.9.
The possible outcomes are (D and not D) or (not D and D).
P(Tieinonematch)=P(Dinmatch1andnotDinmatch2)+P(notDinmatch1andDinmatch2)
P(Tieinonematch)=(P(D)×P(notD))+(P(notD)×P(D))
P(Tieinonematch)=(0.1×0.9)+(0.9×0.1)
P(Tieinonematch)=0.09+0.09=0.18
Alternatively, this includes outcomes WD, LD, DW, DL:
P(Tieinonematch)=P(WD)+P(LD)+P(DW)+P(DL)
P(Tieinonematch)=(0.6×0.1)+(0.3×0.1)+(0.1×0.6)+(0.1×0.3)
P(Tieinonematch)=0.06+0.03+0.06+0.03=0.18
The probability of a tie in one match is 0.18.
3 done, 2 left today. You're making progress.