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Writing expressions??! How? (3 marks)

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    Can someone please explain, what to think/ do when writing an expression?

    For example for this question.

    I have wrote
    Ali
    3 more
    2 hours less
    72 components

    Beth
    72 components

    How do I write the expression. (part i)
    And then please can you go through the rest of the question.

    Once I understand what to think, when writing an expression and learn how to do the other parts, it will be a lot more simple!


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    Ali makes 72 components in t hours
    to show how many he makes in 1 hour divide by t
    ie 72/t components in t/t = 1 hour
    Beth makes 72 components in t+2 hours
    divide by t+2

    that should get you started
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    (i) Number per hour = Number/time

    Na = 72/t


    For Nb you need to change t to t+2 as Beth takes 2 hours longer


    Then Nb + 3 = Na and re-arrange
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    (Original post by blueray)
    Can someone please explain, what to think/ do when writing an expression?

    For example for this question.

    I have wrote
    Ali
    3 more
    2 hours less
    72 components

    Beth
    72 components

    How do I write the expression. (part i)
    And then please can you go through the rest of the question.

    Once I understand what to think, when writing an expression and learn how to do the other parts, it will be a lot more simple!


    Question attached

    Click image for larger version. 

Name:	question a.png 
Views:	69 
Size:	39.4 KB 
ID:	145937

    Thanks
    i)
    t the time for Ali to make 72
    then the component per hour
    72/t
    For Beth
    the components per hour
    72/t -3 (3 less per hour)
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    It has all been explained this question... spo I hope that is enough for you.
    (Original post by blueray)
    Can someone please explain, what to think/ do when writing an expression?

    For example for this question.

    I have wrote
    Ali
    3 more
    2 hours less
    72 components

    Beth
    72 components

    How do I write the expression. (part i)
    And then please can you go through the rest of the question.

    Once I understand what to think, when writing an expression and learn how to do the other parts, it will be a lot more simple!


    Question attached

    Click image for larger version. 

Name:	question a.png 
Views:	69 
Size:	39.4 KB 
ID:	145937

    Thanks
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    (Original post by ztibor)
    i)
    t the time for Ali to make 72
    then the component per hour
    72/t
    For Beth
    the components per hour
    72/t -3 (3 less per hour)
    Beth takes longer
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    (Original post by sputum)
    Ali makes 72 components in t hours
    to show how many he makes in 1 hour divide by t
    ie 72/t components in t/t = 1 hour
    Beth makes 72 components in t+2 hours
    divide by t+2

    that should get you started

    (Original post by TenOfThem)
    (i) Number per hour = Number/time

    Na = 72/t


    For Nb you need to change t to t+2 as Beth takes 2 hours longer


    Then Nb + 3 = Na and re-arrange

    (Original post by ztibor)
    i)
    t the time for Ali to make 72
    then the component per hour
    72/t
    For Beth
    the components per hour
    72/t -3 (3 less per hour)

    (Original post by GreenLantern1)
    It has all been explained this question... spo I hope that is enough for you.
    Why would ali be 72/t

    why not 72/t-2 Because it takes him 2 hours less???

    Where am I wrong? Please explain.
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    (Original post by blueray)
    Why would ali be 72/t

    why not 72/t-2 Because it takes him 2 hours less???

    Where am I wrong? Please explain.
    t was defined in the question as the time that Ali takes
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    (Original post by TenOfThem)
    t was defined in the question as the time that Ali takes
    Ok So when would I be correct then, what would the question have to say, for my answer to be correct?
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    (Original post by blueray)
    Ok So when would I be correct then, what would the question have to say, for my answer to be correct?
    if t had been defined as the time that Beth took
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    (Original post by sputum)
    Ali makes 72 components in t hours
    to show how many he makes in 1 hour divide by t
    ie 72/t components in t/t = 1 hour
    Beth makes 72 components in t+2 hours
    divide by t+2

    that should get you started

    (Original post by ztibor)
    i)
    t the time for Ali to make 72
    then the component per hour
    72/t
    For Beth
    the components per hour
    72/t -3 (3 less per hour)

    (Original post by GreenLantern1)
    It has all been explained this question... spo I hope that is enough for you.

    (Original post by TenOfThem)
    Beth takes longer
    Hence derive the equation 3t(t + 2) = 144.

    What does derive mean? How do I do it?
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    I gave you 3 equations in post 3

    combine them

    re-arrange
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    (Original post by blueray)
    ?
    Right, so the number of components that Ali makes per hour is 72/t
    The number of components that Beth makes per hour is 72/t+2.

    Ali makes 3 more per hour, so \frac{72}{t} = \frac{72}{t+2}+3
    So, \frac{72}{t}-\frac{72}{t+2}=3

    Now multiply all the numerators by (t) and (t+2) to get:

    \frac{72(t)(t+2)}{t}-\frac{72(t)(t+2)}{t+2}=3(t)(t+2)

    This is equalise same as: 72(t+2) - 72(t) = 3(t)(t+2)
    Multiply out your brackets to get
    72t+144-72t = 3t(t+2)
    144=3t(t+2)

    This help?

    EDIT: to figure out part iii) multiply out your brackets in the last equation, and rearrange to get a quadratic, then figure out your values of t from there
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    (Original post by CharlieBoardman)
    Right, so the number of components that Ali makes per hour is 72/t
    The number of components that Beth makes per hour is 72/t+2.

    Ali makes 3 more per hour, so \frac{72}{t} = \frac{72}{t+2}+3
    So, \frac{72}{t}-\frac{72}{t+2}=3

    Now multiply all the numerators by (t) and (t+2) to get:

    \frac{72(t)(t+2)}{t}-\frac{72(t)(t+2)}{t+2}=3(t)(t+2)

    This is equalise same as: 72(t+2) - 72(t) = 3(t)(t+2)
    Multiply out your brackets to get
    72t+144-72t = 3t(t+2)
    144=3t(t+2)

    This help?
    All the steps are well done thanks
    But thing I can't get my head round is
    if Ali makes 3 MORE then why is +3 with Beth??
    Shouldn't it be
    72/t +3 = 72/t+2 ??
    Then 72/t - 72/t+2 = -3??????/
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    (Original post by blueray)
    All the steps are well done thanks
    But thing I can't get my head round is
    if Ali makes 3 MORE then why is +3 with Beth??
    Shouldn't it be
    72/t +3 = 72/t+2 ??
    Then 72/t - 72/t+2 = -3??????/
    I see where your confusion comes from look at it this way.

    Components of Ali per hour = 72/t
    Components of Beth per hour = 72/t+2 yes?
    Right, so Ali makes 3 more than Beth per hour, so 72/t is 3 more than 72/t+2. So to make them equal, you need to add 3 onto 72/t+2, giving you the 72/t=(72/t+2)+3

    This explain it ok?
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    (Original post by CharlieBoardman)
    I see where your confusion comes from look at it this way.

    Components of Ali per hour = 72/t
    Components of Beth per hour = 72/t+2 yes?
    Right, so Ali makes 3 more than Beth per hour, so 72/t is 3 more than 72/t+2. So to make them equal, you need to add 3 onto 72/t+2, giving you the 72/t=(72/t+2)+3

    This explain it ok?
    Yeah that makes sense, but why would you want to make them equal? Sorry if I sound silly, I just want to be crystal clear
    Ps I have lots of English literature notes etc, if you want
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    (Original post by blueray)
    Yeah that makes sense, but why would you want to make them equal? Sorry if I sound silly, I just want to be crystal clear
    Ps I have lots of English literature notes etc, if you want
    Just so that you have something to rearrange and work with. When solving something, you generally want 2 equations which are equal to each other, but layed out differently, so that you can rearrange the, to suit the question.

    For example. We used 72/t=(72/t+2)+3, which we could rearrange to get us somewhere.
    72/t=72/t or 72/t+2=72/t+2 would have been useless to us.

    This ok?

    What books are you studying for Lit?
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    (Original post by blueray)
    Yeah that makes sense, but why would you want to make them equal?

    How would you end up with an equation if you did not have 2 things that were equal to each other
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    (Original post by TenOfThem)
    How would you end up with an equation if you did not have 2 things that were equal to each other
    This is precisely the phrase I was looking for! But I ended up rambling on. :curious:
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    (Original post by CharlieBoardman)
    I see where your confusion comes from look at it this way.

    Components of Ali per hour = 72/t
    Components of Beth per hour = 72/t+2 yes?
    Right, so Ali makes 3 more than Beth per hour, so 72/t is 3 more than 72/t+2. So to make them equal, you need to add 3 onto 72/t+2, giving you the 72/t=(72/t+2)+3

    This explain it ok?
    If it's 3 more isn't it times 3?As you have 3 more lots?

    (Original post by CharlieBoardman)
    What books are you studying for Lit?
    Inspector calls and of mice and men.

    (Original post by TenOfThem)
    How would you end up with an equation if you did not have 2 things that were equal to each other
    Can you help explain charlies point in another way? If I have 2 explanations It would be easier to understand.

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