Problem: For every real number x, let [x] be the greatest integer which is less than or equal to x. If the postal rate for first class mail is six cents for every ounce or portion thereof, then the cost in cents of first-class postage on a letter weighing W ounces is always
Answer Choices:
A. 6W
B. 6[W]
C. 6([ W]−1)
D. 6([ W]+1)
E. −6[−W]
Solution:
If the number of ounces is W=w+p where w is a non-negative integer and 0<p ≤1, then the postage is
6(w+1)=−6(−w−1)=−6[−w−1]=−6[−w−p]=−6[−(w+p)]
=−6[−W] cents.