Andreas completed 5km race in = 3.5 minutes
His sisters time is 1 1/2 or 1 and a half or 1 and 0.5 or 1.5 times more than his time
So, his sisters time= 1 1/2 times Andres time
=1 and a half * Andres time
=1 and 0.5 * Andres time
=1.5 * Andres time
=1.5*3.5
=5.25minutes
So, Andres sister take 5.25 minutes to complete a 5 km race.