Question: A group of keyboard operators are timed and their speeds are recorded in characters per minute. They are found to be approximately N(200,20²). Find the probability that an operator from the group has a speed of:

a). between 180 and 200 char/min,

b). greater than 225 char/min,

c). less than 150 char/min

d) between 205 and 215 char/min?