Janie designed a miniature couch for a dollhouse based on her own couch. Janie's couch is 7 1/2 feet long. The scale of the dollhouse is 1 inch : 2 feet. What is the length of the miniature couch for the dollhouse?
First find the length of the miniature couch in inches by multiplying the length of the real couch in feet by the number of inches per foot: 7.5 feet * 12 inches/foot = <<7.5*12=90>>90 inches
Then divide that number by the number of feet per inch in the dollhouse scale to find the length of the miniature couch: 90 inches / 2 feet/inch = <<90/2=45>>45 inches. Answer: \boxed{45}.