Math

A class has 42 pupils. The ratio of the number of boys to the number of girls is 5 : 2. Find the number of boys in the class.

My understanding is that in order to find the number of boys, you need to find BOTH genders first, and so I could only get up to the number of GIRLS, which I did: 42 divided by 2 = 21
42 divided by 5 = 8.4
But now I'm stuck...
Please help and see if my understanding is correct...

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  1. boys : girls = 5:2
    So, if there are 5x boys, there are 2x girls
    5x+2x = 42
    x = 6

    Now what do you say?

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  2. So basically the number of boys is 6?
    And so is girls??

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  3. NO!
    I solved for the value of x.
    Now go back and read what I said about the number of girls and boys.

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    oobleck
  4. Ohhhh I get it

    So 5x = 5 x 6 = 30 (BOYS)
    And 2x = 2 x 6 = 12 (GIRLS)

    So the number of boys is 30 yes?

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  5. that's better.

    Consider a "group" of students to be 5 boys and 2 girls.
    x is the number of such groups in the class.

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    oobleck

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