Skill: Add multi-digit whole numbers

Line up the numbers by place value: ones under ones, tens under tens, hundreds under hundreds, and so on. Then add from right to left. If a column totals $10$ or more, regroup: write the ones digit and carry the extra ten to the next column.

Example:

$$\begin{array}{r} 47{,}586\\ + 26{,}739\\ \hline \end{array}$$

1. Ones: $6+9=15$. Write $5$ in the ones place and carry $1$ ten.

2. Tens: $8+3+1=12$. Write $2$ in the tens place and carry $1$ hundred.

3. Hundreds: $5+7+1=13$. Write $3$ in the hundreds place and carry $1$ thousand.

4. Thousands: $7+6+1=14$. Write $4$ in the thousands place and carry $1$ ten-thousand.

5. Ten-thousands: $4+2+1=7$. Write $7$.

So,

$$\begin{array}{r} 47{,}586\\ + 26{,}739\\ \hline 74{,}325 \end{array}$$

Therefore, $\boxed{47{,}586+26{,}739=74{,}325}$.

To check, round the numbers:

$$47{,}586\approx 48{,}000,\qquad 26{,}739\approx 27{,}000$$

Since $48{,}000+27{,}000=75{,}000$, the exact answer $74{,}325$ is reasonable.