1. A machine is used to produce the 3-metre barge poles sold by the You Would Touch It With One Of Ours barge pole company.  The actual length, $L$ m, of the barge poles is normally distributed with mean 3 m, standard deviation $\sigma$ m, and interquartile range 0.01712 m.

Twenty of the barge poles are chosen at random.

Find the probability that at most two of the barge poles will be shorter than 3 m by 1 cm or more.