The size of stones used in a 'Concrete blend' are Normally Distributed, with a Mean diameter of 19.5mm and a Standard Deviation of 1.8mm. (P1,K1,K12,K24) (a) What is the probability that a stone taken at random will have a diameter greater than 18mm? (b) The smallest 15.15% of the stones are to be removed by passing them over a sieve. What size should the holes in the sieve' be? (ie: Below what size will the stones be rejected?)