4a) Determine whether a discrete or continuous random variable is the best model for each of the following:

i)The duration of a call at a mobile phone customer care service is_____________.

ii)The number of busy representatives at a mobile customer care service at a time t is_____________.

4b) The writing time in minutes at a popular bakery shop has probability density function f(x) = 0.1exp(-0.1x), x>0.

i)Determine f(x)

Choose from one of the following and show your work.

1)F(x) = 1-exp(-0.1x) for x> 0

2) F(x) = 0.1exp(-0.1x) for x> 0

3) F(x) = 1-0.1exp(-0.1x) for x> 0

ii) Determine P(X<10)