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    i have to work out :


    the sum of Ann and freds ages is 28. in 7 seven years time ann will be twice as old as fred. how old are they now?
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    a + f = 28


    In 7 years time Ann will be a + 7
    How old would Fred be
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    So the equations are

    a + f = 28
    a + 7 = 2(f + 7)
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    yes ive worked out A+7=2f but what are their ages?
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    a + 7 is not = to 2f
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    (Original post by mmmpie)
    So the equations are

    a + f = 28
    a + 7 = 2f
    Shouldn't the second equation be a+7=2(f+7)?
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    (Original post by Gemini92)
    Shouldn't the second equation be a+7=2(f+7)?
    Whoops. Yes

    Best edit to avoid confusion...
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    please can some one answer this GCSE level question i need the equations and their ages
    thank you
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    the equations have been given
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    If we just solve it for you, that doesn't help you learn how to do it.

    First construct the equations, which are

    a + f = 28

    a + 7 = 2(f + 7)

    Then I would simply the second one my multiplying out the bracket.

    Spoiler:
    Show


    So the second equation becomes

    

a + 7 = 2f + 14

    then simplifying a bit more

    

a = 2f + 7



    Then you can use substitution to eliminate one of the variables. Do you know how to do that?
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    bump

    can someone explain substitution to get the answer for this question
    thanks.
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    (Original post by Jed123)
    bump

    can someone explain substitution to get the answer for this question
    thanks.
    The idea behind substitution is that if you have two equations in two variables, you're able to rearrange one such that it gives you a valid expression for one of your variables. You can then use this to rewrite your other equation in terms of a single variable, and thusly solve it.

    For example, (I'm not going to do it for you, but here's a similar question...that you could probably find if you looked in your textbook)
    Spoiler:
    Show

    Let's take

    x + y = 1
    2x + 4y = 3

    From the first equation, we can rearrange to get y = 1 - x

    We can then rewrite the second equation: 2x + 4(1-x) = 3

    Simplifying the above we get to -2x = -1 from which you should be able to solve for x giving x = \frac{1}{2}

    Then, we know that x + y = 1, so substituting in x, we get that y is also 1/2.


    Can you answer your question now?
 
 
 
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