puzzle to puzzle you

a three digit lock has gone defective.....
if any two digit are correct you can be granted access
find the minimum no of trials that will make you get through the door

my guess is 10*10*10 !!!1

it should be 973.
explaination:
total ways 10*10*10
total ways by which 2 of the 3 digits are correct 3*(1*1*9) =27
total ways by which all 3 digits are correct=1
total ways for granting access=28
remaining failure ways=972
hence minimum trials required to get through the door is 973

i think that will be maximum possible trials before solution..