Ram walks to school from home every morning and it takes him 30 minutes.Once on his way he realized that he had forgotten his physics book at home.If he continued walking to school at the same speed,he would be there 12 minutes before the bell.But he went back home for the physics book and reached the school 6 minutes after the bell.Assuming he had walked all the way with his usual speed,the fraction of the way to school he had covered till the moment he turned back is