77....724
where the 7 is repeated as many times as you like, making the number [possibly] infinite.
However, I suspect the question requires a three digit number consisting of the digits of the set {2, 4, 7} used once each: 724
The largest number with no repeated digits is 9,876,543,210 although it is 10 digits long, the largest 3 digit number with no repeated digits is 987
999
The largest three digit prime number whose digits are all primes is 773.
975
995
The largest number with no repeated digits is 9,876,543,210 although it is 10 digits long, the largest 3 digit number with no repeated digits is 987
The largest number with three digits is 999.
999
The largest three digit prime number whose digits are all primes is 773.
975
That would be 999.
995
992
9998888
How about: 773
999 is the largest 3 digit number because each of the three digits is the largest possible value (9). Whole number simply means that there is no decimal part or fraction.
972.