A silicon integrated circuit chip contains 5000 ostensibly identical transistors. Measurements are made of the current gain of each transistor. The measurements have a mean of 20.0 and a standard deviation of 1.5. The probability distribution of the measurements is Gaussian. 

(a) Write down an expression for the number of transistors on the chip, which have a current gain between 19.5 and 20.5. 

(b) Show that this number of transistors with a current gain between 19.5 and 20.5 is approximately 1300. 

(c) Calculate the number of transistors that have a current gain of 17 or more (this is the minimum current gain necessary for a transistor to be able to drive the succeeding stage of the circuit in which the chip is used).