Addition
Combine numbers into a sum · 덧셈
1. What Is Addition?
Addition combines two or more numbers into a single total called the sum. The numbers being added are addends, and the result answers “how many are there altogether?” — whether you are pooling quantities, measuring a combined length, or stepping forward on a number line.
Addition is the first of the four basic operations and the foundation for all the others: multiplication is repeated addition, and subtraction is its exact reverse.
덧셈은 둘 이상의 수를 합쳐 하나의 합으로 만드는 연산입니다. 더하는 수를 가수(addend), 결과를 합(sum)이라 하며, "모두 합치면 얼마인가"에 답합니다. 곱셈(반복 덧셈)과 뺄셈(덧셈의 역)의 토대입니다.
2. The Column Algorithm & a Worked Example
Line the numbers up by place value (ones under ones, tens under tens) and add each column right to left. When a column total reaches 10 or more, write the ones digit and carry the tens digit into the next column.
Worked example. Add 376 + 248:
- Ones: 6 + 8 = 14 → write 4, carry 1.
- Tens: 7 + 4 + 1 (carry) = 12 → write 2, carry 1.
- Hundreds: 3 + 2 + 1 (carry) = 6 → write 6.
So 376 + 248 = 624.
자릿값을 맞춰 오른쪽부터 더하고, 합이 10 이상이면 일의 자리만 적고 십의 자리는 다음 칸으로 받아올립니다. 예: 376 + 248 → 일 14(4 올림1), 십 12(2 올림1), 백 6 = 624.
3. Faster Mental Strategies
The column method always works, but for mental math three strategies are quicker:
- Bridge to ten. Split an addend to reach a round number first: 47 + 38 → 47 + 3 = 50, then 50 + 35 = 85.
- Compensation. Round up, then correct: 47 + 38 = 47 + 40 − 2 = 85.
- Left to right. Add big place values first: (40 + 30) + (7 + 8) = 70 + 15 = 85.
All three reach the same total; skilled calculators pick whichever fits the numbers. See the parent arithmetic guide for more.
암산에서는 친근한 수 만들기(47+3=50→85), 보정(47+40−2=85), 왼쪽부터 더하기((40+30)+(7+8)=85)가 더 빠릅니다. 상황에 맞게 골라 쓰면 됩니다.
4. Key Properties
- Commutative. a + b = b + a — order never changes the sum.
- Associative. (a + b) + c = a + (b + c) — grouping does not matter.
- Additive identity. a + 0 = a — adding zero changes nothing.
- Works beyond whole numbers. The same rules apply to decimals, fractions, and negatives (align decimal points; a + (−b) is subtraction).
덧셈은 교환법칙(a + b = b + a), 결합법칙((a + b) + c = a + (b + c)), 항등원(a + 0 = a)을 만족하며, 소수·분수·음수에도 같은 규칙이 적용됩니다(소수점 정렬, a + (−b)는 뺄셈).
5. Frequently Asked Questions
How do you add numbers with carrying? Add each column right to left; when a column reaches 10 or more, write its ones digit and carry the tens digit into the next column.
Is addition commutative? Yes — a + b always equals b + a, so you can add in any order.
How do you add decimals? Line up the decimal points (so place values match), then add column by column exactly as with whole numbers.
각 칸을 오른쪽부터 더하고 10 이상이면 받아올림합니다. a + b = b + a 로 순서는 무관합니다. 소수는 소수점을 맞춰 정렬한 뒤 정수처럼 더합니다.
Ready to practice? Drill addition and the other operations on C:Arith, or review the full arithmetic reference and the related subtraction, multiplication, and division.