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Math Help - Finding a percentage of a quantity

  1. #1
    Member Sazza's Avatar
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    Finding a percentage of a quantity

    I'm wondering, because i'm doing this: 30% of 360m

    I already know for example: 6%of $20 = 6/100 x 20/1
    = 120/100
    = $1.20
    but when i'm doing: 30% of 360m = 30/100 x 360/1 (is that right? were mean't to be simplifying i think)

    But when i multiply 30 by 360 i get: 10'800
    How would i lay out my question! Because i'v converted the percentage and quantity to fraction.
    Multiplyed and simplifyed (i hope)

    And another one i'm puzzling over is: 75% of $1240
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  2. #2
    Member Sazza's Avatar
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    also i'm having trouble with this: I have to find the simple interest on: $620 at 8.5% p.a. for 2 years.

    and $3500 at 9% p.a. for 3 years, 9 months. how would i do that?
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  3. #3
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    Quote Originally Posted by Sazza View Post
    I'm wondering, because i'm doing this: 30% of 360m

    I already know for example: 6%of $20 = 6/100 x 20/1
    = 120/100
    = $1.20
    but when i'm doing: 30% of 360m = 30/100 x 360/1 (is that right? were mean't to be simplifying i think)

    But when i multiply 30 by 360 i get: 10'800
    How would i lay out my question! Because i'v converted the percentage and quantity to fraction.
    Multiplyed and simplifyed (i hope)

    And another one i'm puzzling over is: 75% of $1240

    The hard way

    30/100 x 360/1 = 30/10 x 36/1 = (multiply across) 108

    The ease way to do this would be to just do:
    .3 x 360 = 108
    also
    .75 x 1240 = 930 or using your method

    75/100 x 1240/1 = 75/10 x 124/1 = 930
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  4. #4
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by nertil1 View Post
    The hard way

    30/100 x 360/1 = 30/10 x 36/1 = (multiply across) 108

    The ease way to do this would be to just do:
    .3 x 360 = 108
    or simply 3 * 36. since 30/10 = 3

    before actually multiplying the fractions, you want to cancel as much as possible to minimize difficulties in computation
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  5. #5
    Member Sazza's Avatar
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    also i'm having trouble with this: I have to find the simple interest on: $620 at 8.5% p.a. for 2 years.

    and $3500 at 9% p.a. for 3 years, 9 months. how would i do that?
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  6. #6
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by Sazza View Post
    also i'm having trouble with this: I have to find the simple interest on: $620 at 8.5% p.a. for 2 years.

    and $3500 at 9% p.a. for 3 years, 9 months. how would i do that?
    Simple \mbox { } Interest = Principal \times Rate \times Time

    Simple Interest is the interest we gain. the principal is the amount of money we start with. the rate is the percentage interest (written as a fraction) we gain per unit time and the time is how long we are earning interest for in terms of the number of interest periods

    note that 3 years 9 months is 3.75 years
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