A person learning certain skills involving repetition tends to learn quickly at first. Then learning tapers off and skill acquisition approaches some upper limit. Suppose the number of symbols per minute that a person using a keyboard can type is given by

ƒ(t) = 250 - 120(2.8)^-0.5t,

where t is the number of months the operator has been in training. Find each value to the nearest whole number.

(a) ƒ(2) 

(b) ƒ(4) 

(c) ƒ(10)

(d) What happens to the number of symbols per minute after several months of training?