If k is a positive integer, then k@ is defined as the product of all the fractions of the form 1/S, where S is a positive integer not greater than k. What is the value of 5@/4@?
A. 1/5 B. 4/5 C. 1 D. 5/4 E. 5
(A) Since k@ is defined as the product of all fractions 1/S, where S ranges from 1 to k, inclusive, 5@ = (1/1) × (1/2) × (1/3) × (1/4) × (1/5) 4@ = (1/1) × (1/2) × (1/3) × (1/4)
5@/4@ = (1/1) × (1/2) × (1/3) × (1/4) × (1/5) (1/1) × (1/2) × (1/3) × (1/4)
All of the fractions cancel out except for the 1/5, so the correct answer is choice (A).  Can we understand "A is the product of X & Y" as "A = X × Y", not that A is some other combination forms of X and Y?
