Can anyone please "check" my following questions answers...
Q How many strings of four decimal digits
a) do not contain the same digit twice
my ans: 4 x 9^2
b) end with an even digit
my ans: 5 x 10^3
c) have exactly three digits that are 9s
my ans: 4 x 9
Thanks for the help!
[QUOTE=robocop_911;151794]Q How many strings of four decimal digits
a) do not contain the same digit twice
my ans: 4 x 9^2 NO
b) end with an even digit
my ans: 5 x 10^3 YES
c) have exactly three digits that are 9s
my ans: 4 x 9 YES
Part (a) is a simple permutation: (10)(9)(8)(7). No repeated digits.