Drill used in the manufacture of the engine parts is designed to have seven speeds. The range of hole sizes anticipated is from 6mm to 25mm.
You have been asked to determine the six spindle speeds (rev/min) given that the cutting speed is 20m/min.

These spindle speeds are to be arranged in:
a) arithmetic progression 
b) geometric progression 

Note: N=1000s/pi x D, N=spindle speed (rev/min), s=cutting speed (m/min), D=hole diameter (mm)