Hi, I'm stuck with this, if anyone can help, it'll be awesome!

1. Four-fifths of all volunteers working in a charity shop are over 50. If two volunteers are chosen at random, what is the probability that one of them is over 50, but the other one is not?

- 0.04
- 0.2
- 0.16
- 0.32
- None of the above

2. A producer of 'home-made' biscuits is known to produce biscuits whose thicknesses are Normally-distributed. If the mean thickness is 4mm with a standard deviation of 0.6mm, approximately what proportion of biscuits will be thicker than 5mm?

- 0.9525
- 0.0446
- 0.0475
- 0.4325
- None of the above

what is the quickest way or formula or working it out?