Skill: Subtract 3-digit numbers with regrouping

To subtract 3-digit numbers, line up the hundreds, tens, and ones. Start subtracting in the ones place.

Example:

$$\begin{array}{r} 503\\ -\ 278\\ \hline \end{array}$$

1. Ones: We need to subtract $8$ ones from $3$ ones. Since $3$ is too small, regroup.

   • There are no tens to trade, so trade $1$ hundred for $10$ tens.
   • Now $5$ hundreds becomes $4$ hundreds, and there are $10$ tens.
   • Trade $1$ of those tens for $10$ ones. Now there are $9$ tens and $13$ ones.

   Subtract the ones:

$$13-8=5$$

2. Tens: Subtract the tens:

$$9-7=2$$

3. Hundreds: Subtract the hundreds:

$$4-2=2$$

So,

$$\begin{array}{r} 4\ 9\ 13\\ 5\ 0\ 3\\ -\ 2\ 7\ 8\\ \hline 2\ 2\ 5 \end{array}$$

Therefore,

$$503-278=\boxed{225}$$

Regrouping does not change the number’s value: $503$ is still $4$ hundreds, $9$ tens, and $13$ ones.