Math!Quick!20 point!Desmond...

I suppose this is "If Desmond gives $160 to [ Jay ]".

Let D be the amount Desmond has and J be the amount of Jay.

D + J = 800
D = 800 - J

If Desmond gives $160 to Jay, Jay will have 1.5 times as much as Desmond has

(J+160)/(D-160) = 1.5 = 3/2
2(J+160) = 3(D - 160)
2J + 320 = 3[(800 - J) - 160]
2J + 320 = 3(800 - J) - 3(160)
2J + 320 = 2400 - 3J - 480
2J + 320 = 1920 - 3J
2J + 3J = 1920 - 320
5J = 1600
J = 1600/5 = 320
D = 800 - J = 480

Checking :

(J+160)/(D-160) = (320+160)/(480-160) = 480/320 = 1.5

2014-01-27 00:38:03 補充：
If the question is "If Desmond gives $160 to Joy". then

D + J = 800
D = 800 - J

If Desmond gives $160 to Joy, Jay will have 1.5 times as much as Desmond has

J/(D-160) = 3/2

2J = 3(D-160) = 3D - 480 = 3(800-J) - 480 = 2400 - 3J - 480 = 1920 - 3J

2014-01-27 00:40:25 補充：
2J = 1920 - 3J
5J = 1920
J = 1920/5 = 384
D = 800 - J = 800 - 384 = 416

D+J = 416+384 = 800

J/(D-160) = 384/(416-160) = 384/256 = 1.5