Answer
$413$
Work Step by Step
$278 + 135$
Start at the right of each number and add the ones digits
$8 + 5 = 13$ ones
Regroup the $13$ ones as $1$ ten and $3$ ones
Write the $3$ ones in the ones column.
Write the $1$ ten in the tens column.
Add the tens digits next including the regrouped $1$.
$1 + 7 + 3 = 11$ tens
Regroup the $11$ tens as $1$ hundred and $1$ ten
Write the $1$ ten in the tens column.
Write the $1$ hundred in the hundreds column
Add the hundreds column next including the regrouped 1
$1 + 2 + 1 = 4$ hundreds
Write the $4$ hundreds in the hundreds column
The sum of the two numbers is $413$
