chun chi asked in 科學及數學數學 · 1 decade ago

form 4 Math

Kelvin has $P and Jacqueline has twice as much. Kelvin spends $50 a day while Jacqueline spends $80 and pays on extra $10 to Kelvin a day.

(a) Find the total amou of money they have after x days.

(b) If after x days, Kelvin has $300 more than twice the amount of Jacqueline, find a relation connecting P and x.

(c) If Kelvin has $7000 at the beginning, find the value of x so that Kelvin has twice the amount of jacqueline.

1 Answer

Rating
  • wy
    Lv 7
    1 decade ago
    Best Answer

    Amount of Kelvin at the beginning = P

    Amount of Jacq at the beginning = 2P

    After 1 day, Kelvin amount = P - 50 +10 = P + 40.

    Jacq. amount = 2P - 80 - 10 = 2P - 90.

    After x days, Kelvin amount = P -50x + 10x = P -40x.

    Jacq. amount = 2P - 80x - 10x = 2P - 90x.

    (a) Total amount after x days = P - 40x + 2P - 90x = 3P - 130x.

    (b) (P - 40x) - 2(2P - 90x) = 300

    P - 40x - 4P + 180x - 300 = 0

    140x - 3P - 300 = 0.

    (c) (P - 40x) = 2(2P - 90x).

    P - 40x = 4P - 180x

    3P = 140x

    x = 3P/140.

    Now P = 7000, therefore, x = 3 x 7000/140 = 150 days.

    2008-07-31 11:12:39 補充:

    Correction: Line 3 should be P - 40.

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