Select the Appropriate Sign: Comparing 990,090 with 999,000

To solve this problem, we'll compare the numbers $990,090$ and $999,000$ digit by digit from left to right.

• Step 1: Start at the hundred-thousands place: - The first number has 9, and the second number also has 9, so they are equal.
• Step 2: Move to the ten-thousands place: - The first number has 9, and the second number also has 9; still equal.
• Step 3: Move to the thousands place: - The first number has 0, and the second number has 9; 9 is greater than 0.

Since the thousands digit (0 vs 9) determines the comparison, we conclude that 999,000 is greater than 990,090.

Therefore, the correct comparison is $990,090$ < $999,000$, so the appropriate sign is <.