47) The ratio of the pitch circle diameter in millimetres to the number of teeth, is called

48) The minimum number of teeth on the pinion which will mesh with any gear without interference for 20 degree full depth involute teeth will

49) In a simple train of wheels, the velocity ratio ______ the intermediate wheels.

50) When the axes of the first and last wheels are co-axial, then the train is known as ______

51) When the axes of the shafts, over which the gears are mounted, move relative to a fixed axis, then the train is known as reverted gear train.