The second movie was 2*.5=<<2*.5=1>>1` hour longer than the first movie
So the second movie was 2+1=<<2+1=3>>3 hours long
That means the first two movies had a combined time of 3+2=<<3+2=5>>5 hours
So the last movie had a length of 5-1=<<5-1=4>>4 hours
That means the marathon lasted 5+4=<<5+4=9>>9 hours
#### 9