Which is greater, the greatest whole number with 4 digits or the least whole number with 5 digits?

The answer would be the least whole number with 5 digits. You have to base it on the place values of each digit of a number. As the number of digits increases, the value also increases. For a number with 4 digits, the greatest value would be a multiple of 1,000. For a number with 5 digits, the greatest value would be a multiple of 10,000. Hence, no matter what is the multiple, 10,000 would always be far greater than 1,000.