Turn on thread page Beta
    • Thread Starter
    Offline

    0
    ReputationRep:
    A game uses an unbiased die with faces numbered 1 to 6. The die is thrown once. If it shows 4 or 5 or
    6 then this number is the final score. If it shows 1 or 2 or 3 then the die is thrown again and the final
    score is the sum of the numbers shown on the two throws.
    (i) Find the probability that the final score is 4.

    Confused why the answer is

    1/6 + 3*(1/6)^2

    I would have thought the answer was:
    1/6 + 4*(1/6)^2
    Because u can have
    a 4 (1,3)(3,1)(2,2)(2,2)
    • Community Assistant
    Online

    18
    ReputationRep:
    Community Assistant
    (Original post by ineedhelpwithph)
    A game uses an unbiased die with faces numbered 1 to 6. The die is thrown once. If it shows 4 or 5 or
    6 then this number is the final score. If it shows 1 or 2 or 3 then the die is thrown again and the final
    score is the sum of the numbers shown on the two throws.
    (i) Find the probability that the final score is 4.

    Confused why the answer is

    1/6 + 3*(1/6)^2

    I would have thought the answer was:
    1/6 + 4*(1/6)^2
    Because u can have
    a 4 (1,3)(3,1)(2,2)(2,2)
    You put (2,2) twice.
    Offline

    9
    ReputationRep:
    (2,2) is the same you don't count it twice. It's not the same as (1,3) and (3,1) because the order matters since it makes a difference as you either get a one first or three whereas if you score a two both times it's the same.
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by Han-Mingi)
    (2,2) is the same you don't count it twice. It's not the same as (1,3) and (3,1) because the order matters since it makes a difference as you either get a one first or three whereas if you score a two both times it's the same.
    Thanks just wondering because there are 2 possible ways to get 2,2 how come you don't count it twice?
    Offline

    9
    ReputationRep:
    (Original post by ineedhelpwithph)
    Thanks just wondering because there are 2 possible ways to get 2,2 how come you don't count it twice?
    Your list was 4(1,3)(3,1)(2,2)(2,2) but you see getting (2,2) is the same as the first time. It's not the same as getting (1,3) and (3,1), Why? You ask. Well just take a look at the number order it's different but with your (2,2) and (2,2) it's the same so you can't count (2,2) twice. It's like saying give me using all 1,2,3 all the possible combinations to add to four, well there's 1+3, 3+1, 2+2, 2 is the same as 2 but 1 does not equal
    3 hence you can swap the order for 1 and 3 but not for 2+2 because it's the same
 
 
 
The home of Results and Clearing

2,816

people online now

1,567,000

students helped last year

University open days

  1. SAE Institute
    Animation, Audio, Film, Games, Music, Business, Web Further education
    Thu, 16 Aug '18
  2. Bournemouth University
    Clearing Open Day Undergraduate
    Fri, 17 Aug '18
  3. University of Bolton
    Undergraduate Open Day Undergraduate
    Fri, 17 Aug '18
Poll
Do you want your parents to be with you when you collect your A-level results?
Help with your A-levels

All the essentials

The adventure begins mug

Student life: what to expect

What it's really like going to uni

Rosette

Essay expert

Learn to write like a pro with our ultimate essay guide.

Uni match

Uni match

Our tool will help you find the perfect course for you

Study planner

Create a study plan

Get your head around what you need to do and when with the study planner tool.

Study planner

Resources by subject

Everything from mind maps to class notes.

Hands typing

Degrees without fees

Discover more about degree-level apprenticeships.

A student doing homework

Study tips from A* students

Students who got top grades in their A-levels share their secrets

Study help links and info

Can you help? Study help unanswered threadsRules and posting guidelines

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.