Return to the example used in the chapter of two machines filling bottles of shampoo. One machine had a mean of 500 ml, SD 10 ml, the other a mean of 750 ml, SD 15 ml. For each machine calculate the lower and upper amounts (in ml) between which:

(a) 90 per cent of all output will fall;

(b) 95 per cent of all output will fall;

(c) 99 per cent of all output will fall.