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Math Help - Word Problem help

  1. #1
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    Word Problem help

    At a certain high school, the psychology class consists of 60% of the senior class. In the psychology class, 40% of the students are boys, and there are 90 girls in this class. What is the total number of students in the senior class at this high school?

    I know the answer should be 250 but how can I show it algebraically?
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  2. #2
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    Thumbs up Re: Word Problem help

    Hello, mjoshua!

    At a certain high school, the Psychology class consists of 60% of the senior class.
    In the Psychology class, 40% of the students are boys, and there are 90 girls in this class.
    What is the total number of students in the senior class at this high school?

    Let N = total number in the senior class.

    60% of N are in the Psych class: . 0.6N \,=\,P .[1]

    In the Psych class, 60% are girls: . 0.6P \,=\,90 \quad\Rightarrow\quad P \,=\,150 .[2]

    Substitute [2] into [1]: . 0.6N \:=\:150 \quad\Rightarrow\quad N \:=\:\frac{150}{0.6}

    Therefore: . N \:=\:250
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