Problem Solving

what is the probability that the sum of two different numbers randomly picked (without replacement) from the set S = {1,2,3,4} is 5
a)1/5
b)3/16
c)1/4
d)1/3
e)1/2

d
explanation: 4.3 = 12 ways to select two numbers
where as 4 ways to select two numbers that sum to 5 (1+4, 4+1, 2+3, 3+2)
4/12 = 1/3
Is their any other way to do this question?

this question is from Nova Gmat math bible...is it a good book for practice? the book is poorly edited but can i use it as a supplement?