A factory manufactures ball-pens and all products are sold at Tk. 10 per piece. If for manufacturing x pieces of ball-pens total cost,   2 c x x x    30 2 0.02 . A. (a) How many pieces to be produced for maximum income? (b) What will be the maximum income?

The distribution of the amount of money spent by students for textbooks in a semester is approximately normal in shape with a mean of $235 and a standard deviation of $20. according to the standard deviation rule, how much did almost all (99.7%) of the students spend on textbooks in a semester?