Three-Digit Addition and Subtraction Word Problems

Word problems are just math puzzles hidden inside real-world stories! When we solve three-digit addition and subtraction word problems, we are figuring out totals and differences using numbers up to 999.

Clue Words to Look For

Before you start calculating, read the story carefully and look for clue words that tell you whether to add or subtract.

• Addition Clue Words (Add them together): in all, total, altogether, combined, sum.
• Subtraction Clue Words (Take away or compare): left, remain, difference, how many more, gave away.

Solving an Addition Word Problem

Let's look at a real-world example of adding three-digit numbers:

Problem: A school has 356 boys and 278 girls. How many students in all?

1. Find the clue: The phrase "in all" tells us we need to add.
2. Write the equation: $356 + 278 = ?$
3. Line up and solve: Line up the hundreds, tens, and ones.
   • Add the ones: $6 + 8 = 14$ (Write 4, regroup 1 ten)
   • Add the tens: $5 + 7 + 1 = 13$ (Write 3, regroup 1 hundred)
   • Add the hundreds: $3 + 2 + 1 = 6$

Answer: There are 634 students in all.

Solving a Subtraction Word Problem

Now let's try a problem where things are taken away:

Problem: The library had 500 books. 187 were checked out. How many remain?

1. Find the clue: The word "remain" tells us we need to subtract.
2. Write the equation: $500 - 187 = ?$
3. Line up and solve: Line up the place values. Since you cannot subtract 7 from 0, you need to regroup (borrow) across the zeros.
   • Regroup 500 into 4 hundreds, 9 tens, and 10 ones.
   • Subtract the ones: $10 - 7 = 3$
   • Subtract the tens: $9 - 8 = 1$
   • Subtract the hundreds: $4 - 1 = 3$

Answer: There are 313 books remaining.

Tips for Success

• Always read the whole problem first.
• Underline the important numbers and the clue words.
• Take your time lining up your hundreds, tens, and ones perfectly before doing the math!