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Help with Math.

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1. I've posted this question before (once, the other post wasn't me)and I have still got no help.


Peg spends $7.50 a week for grapefruit. When grapefruit are out of season, she gets 1 fewer grapefruit than when they are in season. If the price decreases by $3 per dozen in season, how many dollars will it cost to buy a dozen grapefruit out of season?

  • Help with Math. -

    Let the price per dozen in season be $x
    let the price per dozen out of season be $(x+3)

    So in season for $7.50 she can buy 7.5/x dozen
    or 90/x grapefruits

    Out of season for $7.50 she can buy 7.5/(x+3) dozen or 90/(x+3) grapefruits

    so 90/x - 90/(x+3) = 1

    multiply by x(x+3)
    90(x+3) - 90x = x(x+3)
    expand and simplify
    x^2 + 3x - 270 = 0
    (x+18)(x-15) = 0
    x = -18 or x = 15 , but clearly x > 0

    price out of season was defined as x+3
    so out of season they sold at $18 per dozen, WOW!

    check:
    in season she could buy 7.5/15 = .5 dozen or 6 grapefruits
    out of season she could buy 7.5/18 or .4166667 dozen or 5 grapefruits

    is 6-5 = 1 ? YES

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