# 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.

Rating

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.