Long multiplication by one digit
Long multiplication by one digit is a way to multiply a whole number by a single-digit number, one place at a time. It helps you keep track of each partial product and place value.
Method
- Write the numbers neatly with the larger number on top and the single digit underneath.
- Start with the ones place of the top number.
- Multiply that digit by the bottom number.
- Write the ones digit of the product below the line and carry any tens to the next place.
- Repeat for each place value from right to left.
- If there is a carried number at the end, write it down as the leading digit of the answer.
Check your work
- Estimate the answer first to see if your final result is reasonable.
- Multiply in the opposite order if that is easy, to confirm the product.
- Recompute any step where you had to carry.
Helpful tip
Keep the columns aligned. Most mistakes in long multiplication come from skipping a carry or writing a digit in the wrong place.