Both take 10 credits for fall 2008

Bettey GPA 2.0
Total earned points 2.0*10=20

Amy GPA 1.9
Total earned points 1.9*10 =19

Spring 2009

Betty takes 10 credits and get 4.0 but Amy takes 100 credits and gets 3.9

Betty total earned points =4*10=40

Amy total earned points = 3.9*100 = 390

Combined beety gpa (20+40)/(10+10)=3.0

Combines amy gpa (19+390)/(10+100) which is greater than 3.

I hav taken 100 because it is a math problem not a day to day practical problem