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Math Help - do i add the 25% then * it by 306?

  1. #1
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    do i add the 25% then * it by 306?

    1. An instrument store gives a 10% discount to all students off the original cost of an instrument. During a back to school sale an additional 15% is taken off the discounted price. Julie, a student at the local high school, purchases a flute for $306. How much did it originally cost?


    A. $325
    B. $375
    C. $400
    D. $408
    E. $425
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  2. #2
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    Quote Originally Posted by lambofgod View Post
    1. An instrument store gives a 10% discount to all students off the original cost of an instrument. During a back to school sale an additional 15% is taken off the discounted price. Julie, a student at the local high school, purchases a flute for $306. How much did it originally cost?


    A. $325
    B. $375
    C. $400
    D. $408
    E. $425
    No, you wouldn't do 25% because the last 15% is 15% of the 90% of the original. In mathematical terms:

    T(x) = T(0)(1-0.1)(1-0.15) where T(x) is the discounted price and T(0) is the original price. (1-0.1) is the original 10% off and (1-0.15) is the further 15% off

    We know T(x) = 306 and need to find T(0)

    T(0) = \frac{306}{(1-0.1)(1-0.15)} = 400
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    okay im sorta lost, how did you get T(x) = T(0)(1-0.1)(1-0.15) ?

    i thought it said since the original discount was 10% and they added another 15% which = 25%

    then i was taught to do something like .25*306=

    then you get the sum of .25*306 and add it together. any easier way to do this? i cant use the calculator while taking this asvab
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  4. #4
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    e^(i*pi)'s Avatar
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    Quote Originally Posted by lambofgod View Post
    okay im sorta lost, how did you get T(x) = T(0)(1-0.1)(1-0.15) ?

    i thought it said since the original discount was 10% and they added another 15% which = 25%

    then i was taught to do something like .25*306=

    then you get the sum of .25*306 and add it together. any easier way to do this? i cant use the calculator while taking this asvab
    The only way you could add the 15% and the 10% is if they were both off the original price. As the 15% is not off the original price but rather the original discount which means the 15% is off 90% of the original price.
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