Basic operations
The four basic operations are addition (+), subtraction (−), multiplication (×) and division (÷). With numbers up to 100 000 we line up the digits by place value and work carefully, one column at a time.
Key idea / 要点
Add and subtract from the ones column, carrying or borrowing when needed. For × and ÷, keep the place values lined up neatly so no digit is misplaced.
A worked sum
Line up the numbers by place value and add each column, starting from the ones.
Worked example / 例题
Work out 34 210 + 5 780. Add ones: 0 + 0 = 0; tens: 1 + 8 = 9; hundreds: 2 + 7 = 9; thousands: 4 + 5 = 9; ten thousands: 3. Answer = 39 990.
Remember / 记住
- Keep digits lined up by place value.
- Carry when a column is 10 or more.
- Borrow when the top digit is too small to subtract.