Skill: Order whole numbers

To order whole numbers, compare their digits by place value. Start with the greatest place—the hundred-thousands place for numbers up to $1{,}000{,}000$. If those digits are the same, compare the ten-thousands digits, then the thousands, and so on. The first different digit tells you which number is greater.

Example: Arrange these numbers from least to greatest:

$$407{,}215,\quad 470{,}125,\quad 399{,}999,\quad 407{,}251$$

1. Compare the hundred-thousands digits:

   • $407{,}215$ has $4$
   • $470{,}125$ has $4$
   • $399{,}999$ has $3$
   • $407{,}251$ has $4$

   Since $3<4$, $399{,}999$ is the least number.

2. Compare the three numbers that begin with $4$. Their ten-thousands digits are:

   • $407{,}215$ has $0$
   • $470{,}125$ has $7$
   • $407{,}251$ has $0$

   Since $0<7$, $470{,}125$ is the greatest of these three.

3. Compare $407{,}215$ and $407{,}251$. Their digits match through the hundreds place, so compare the tens digits:

   • $407{,}215$ has $1$ ten
   • $407{,}251$ has $5$ tens

   Since $1<5$, $407{,}215<407{,}251$.

Therefore, from least to greatest:

$$\boxed{399{,}999<407{,}215<407{,}251<470{,}125}$$

On a number line, the numbers farther to the left are less, and the numbers farther to the right are greater. To order from greatest to least, simply reverse the order.