Tuesday, February 3, 2009

Multiplying three digit by one digit numbers

How to multiply a three digit number by a one digit number
(e.g. 159 * 7).

  • Place one number above the other so that the ones' place digits are lined up. Draw a line under the bottom number.

  • 159
    7

  • Multiply the two ones' place digits (9 * 7 = 63). This number is larger than 9, so place the six above the tens' place column and place the three below the line in the ones' place column.

  • 6
    159
    7
    3

  • Multiply the digit in the tens' place column (5) by the other number (7). The result is 5 * 7 = 35. Add the 6 to the 35 which equals 41. Place the one from the number 41 below the line and to the left of the other number. Place the 4 above the hundreds' place column.

  • 46
    159
    7
    13
  • Multiply the digit in the hundreds' place column (1) by the digit in the ones' place of the second number (7). The result is 1 * 7 = 7. Add the 4 to the 7 (4 + 7 = 11). Place this below the line and to the left of the other digits.

  • 46
    159
    7
    1113

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