The battery-charging time X (in minutes) of the mobile phones of a certain brand follows an approximately Normal distribution with parameters = 50 minutes and = 5 minutes.(20 marks)

a) Compute the probability that it takes at least 1 hour to charge the battery of amobile phone of that brand.(10 marks)

b) What is the chance that it takes between 45 minutes and 1 hour to charge thebattery of a mobile phone of that brand?(10 marks)