Hey there! Sign in to join this conversationNew here? Join for free
x Turn on thread page Beta
    • Thread Starter
    Offline

    10
    ReputationRep:
    Fahad has 4 different coloured pairs of shoes (white, red, blue and black), 3 different coloured pairs of jeans (blue, black and brown) and 7 different coloured tee shirts (red, orange, yellow, blue, green, white and purple).


    (i) Fahad chooses an outfit consisting of one pair of shoes, one pair of jeans and one tee shirt. How many different outfits can he choose? [1]
    this question confuses me although it just has one mark , so it is supposed to be really simple .
    The answer in the markscheme is 7x3x4=84
    But my question is why ? And why can't I use combination for eg 7C1+4C1+3C1=14
    Please do explain to me why . Any help would be great.
    Posted on the TSR App. Download from Apple or Google Play
    • Study Helper
    Offline

    15
    Study Helper
    (Original post by Sammysammy99)
    Fahad has 4 different coloured pairs of shoes (white, red, blue and black), 3 different coloured pairs of jeans (blue, black and brown) and 7 different coloured tee shirts (red, orange, yellow, blue, green, white and purple).


    (i) Fahad chooses an outfit consisting of one pair of shoes, one pair of jeans and one tee shirt. How many different outfits can he choose? [1] this question confuses me although it just has one mark , so it is supposed to be really simple .
    The answer in the markscheme is 7x3x4=84
    But my question is why ? And why can't I use combination for eg 7C1+4C1+3C1=14
    Please do explain to me why . Any help would be great.
    First off 7x3x4 is the same as 7C1 x 3C1 x 4C1, and you could do it via combinations.

    So, why multply rather than add?

    Because for each choice of one item, you could have any of the other items.

    E.g. for one particular choice of shoes and jeans you could have any of the 7 tee shirts.
    For another choice, again you could any of the 7
    How many combinations of shoes and jeans are there? 4 x 3, and for each of those combinations you could have any of the 7 tee shirts, so 4x3x7.
    • Thread Starter
    Offline

    10
    ReputationRep:
    (Original post by ghostwalker)
    First off 7x3x4 is the same as 7C1 x 3C1 x 4C1, and you could do it via combinations.

    So, why multply rather than add?

    Because for each choice of one item, you could have any of the other items.

    E.g. for one particular choice of shoes and jeans you could have any of the 7 tee shirts.
    For another choice, again you could any of the 7
    How many combinations of shoes and jeans are there? 4 x 3, and for each of those combinations you could have any of the 7 tee shirts, so 4x3x7.
    I still don’t get why you have to multiply them , I’m sorry can u just explain it a bit more about why u have to multiply rather than add ?
    Posted on the TSR App. Download from Apple or Google Play
    • Thread Starter
    Offline

    10
    ReputationRep:
    (Original post by ghostwalker)
    First off 7x3x4 is the same as 7C1 x 3C1 x 4C1, and you could do it via combinations.

    So, why multply rather than add?

    Because for each choice of one item, you could have any of the other items.

    E.g. for one particular choice of shoes and jeans you could have any of the 7 tee shirts.
    For another choice, again you could any of the 7
    How many combinations of shoes and jeans are there? 4 x 3, and for each of those combinations you could have any of the 7 tee shirts, so 4x3x7.
    For example when do we use the add ? If it were add
    Posted on the TSR App. Download from Apple or Google Play
    Offline

    18
    ReputationRep:
    exam solutions has a video that shows you why.
    I'll see if I can find it for you.
    Posted on the TSR App. Download from Apple or Google Play
    • Thread Starter
    Offline

    10
    ReputationRep:
    (Original post by RuthieG101)
    exam solutions has a video that shows you why.
    I'll see if I can find it for you.
    Please tell me if u do find it , I really need the answer. Are u studying statistics too?
    Posted on the TSR App. Download from Apple or Google Play
    • Study Helper
    Offline

    15
    Study Helper
    (Original post by Sammysammy99)
    I still don’t get why you have to multiply them , I’m sorry can u just explain it a bit more about why u have to multiply rather than add ?
    Lets look at a simpler case.

    Suppose you have 3 types of socks - 1,2,3 - and 4 pairs of jeans - a,b,c,d. How many outfits can you make?

    1a, 1b,1c, 1d,
    2a, 2b, 2c, 2d,
    3a, 3b, 3c, 3d.

    That is 3 x 4 = 12 in all.
    • Thread Starter
    Offline

    10
    ReputationRep:
    (Original post by ghostwalker)
    Lets look at a simpler case.

    Suppose you have 3 types of socks - 1,2,3 - and 4 pairs of jeans - a,b,c,d. How many outfits can you make?

    1a, 1b,1c, 1d
    2a, 2b,2c,2d,
    3a,3b,3c,3d.

    That is 3 x 4 = 12 in all.
    I get it now ! Thank you very much . That was really helpful !!
    Posted on the TSR App. Download from Apple or Google Play
    Offline

    18
    ReputationRep:
    im taking s1 in June to finish my a level.

    the video is https://youtu.be/NaDZ0zVTyXQ

    it's for binomial distribution, but shows where all the choices come from
    Posted on the TSR App. Download from Apple or Google Play
    • Thread Starter
    Offline

    10
    ReputationRep:
    (Original post by RuthieG101)
    im taking s1 in June to finish my a level.

    the video is https://youtu.be/NaDZ0zVTyXQ

    it's for binomial distribution, but shows where all the choices come from
    Thank you so much again , you are very kind !
    Posted on the TSR App. Download from Apple or Google Play
    Offline

    18
    ReputationRep:
    no problem.
    I happened to watch it while avoiding my textbook.
    his website is recommended too. he has loads!!
    Posted on the TSR App. Download from Apple or Google Play
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: March 9, 2018
Poll
Do you like carrot cake?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

Equations

How to use LaTex

Writing equations the easy way

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

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.