Call the number you want to find in the form abcd with (a, b, c, d) ∈ A= {0, 1, 2, 3, 4, 5}.
Since abcd is an even number ⇒ d = {0, 2, 4}.
TH1. If d = 0, the number to look up is abc0 Then:
a is selected from the set A\{0}, so there are 5 choices.
b is selected from the set A\{0, a}, so there are 4 choices.
c is selected from the set A\{0, a, b}, so there are 3 choices.
Thus, we have 5.4.3 = 60 numbers of the form abc0
TH2. If d ∈ {2, 4} ⇒ d has 2 choices.
Then, a has 4 choices (other than 0 and d),
b has 4 choices and c has 3 choices.
Thus, we have 2.4.4.3 = 96 numbers to find as above.
So there are all 60 +96 = 156 numbers to find.
Choose answer A
