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There are 40 children in a class. n of them do not wear spectacles. 4/5 of the boys and 2/3 of the girls wear spectacles. Express the number of boys who wear spectacles in terms of n.

  • math -

    b+g = 40
    4/5 b + 2/3 g = 40-n

    2/3 b + 2/3 g = 2/3 * 40
    4/5 b + 2/3 g = 40-n

    (4/5 - 2/3)b = 40-n - 2/3*40
    2/15 b = 40/3 - n
    b = 5(40-3n)/2 = 100 - 15n/2

    Check: suppose n = 10
    b = 25
    g = 15

    boys who wear: 20
    girls who wear: 10

  • math -

    Thank you, Steve.

  • math -

    I dun understand

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