Help with floor and ceiling functions

Need help with the questions below:

Suppose f : **R **→ **Z **where f(x) = the ceiling of 2x − 1.

(a) If A = {x | 1 ≤ x ≤ 4}, find f(A).

For this one I got {1,3,5,7} but one of my friends got {1,2,3,4,5,6,7}. Which one is right?

(c) If C = {−9,−8}, find f−1(C).

For this one I got -2 for both but somebody else got (-9/2, -7/2]. Which one is right?

(d) If D = {0.4,0.5,0.6}, find f−1(D).

For this one I got {4,3} but somebody else got the empty set/nullset. Which one is right?

Suppose f : **R **→ **R **where f(x) = floor of x/2.

(b) If T = {3,4,5}, find f−1(T).

For this one I got zero for all three and somebody else got [6,12).