Calculate normal interval/tail probabilities, a paired probability and an inverse quantile.

The mass of packets of a breakfast cereal is normally distributed with a mean of 750 g and standard deviation of 25 g.

1. Find the probability that a packet chosen at random has mass[5]
   1. less than 740 g;
   2. at least 780 g;
   3. between 740 g and 780 g.
2. Two packets are chosen at random. What is the probability that both packets have a mass which is less than 740 g?[2]
3. The mass of 70% of the packets is more than x grams. Find the value of x.[2]