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Tuesday, 18 January 2011

How to do double digit long division?

How to divide a four digit number by a two digit number (e.g. 4138 ÷ 17):
  • Place the divisor before the division bracket and place the dividend (4138) under it.

  •        
    17)4138

  • Examine the first digit of the dividend(4). It is smaller than 17 so can't be divided by 17 to produce a whole number. Next take the first two digits of the dividend (41) and determine how many 17's it contains. In this case 41 holds two seventeens (2*17=34) but not three (3*17=51). Place the 2 above the division bracket.

  •     2  
    17)4138

  • Multiply the 2 by 17 and place the result (34) below the 41 of the dividend.

  •     2 
    17)4138
       34

  • Draw a line under the 34 and subtract it from 41 (41-34=7). Bring down the 3 from the 4138 and place it to the right of the 7.

  •     2 
    17)4138
       34
        73

  • Divide 73 by 17 and place that answer above the division bracket and to the right of the two.

  •     24 
    17)4138
       34
        73

  • Multiply the 4 of the quotient by the divisor (17) to get 68 and place this below the 73 under the dividend. Subtract 68 from 73 to give an answer of 5. Bring down the 8 from the dividend 4138 and place it next to the 5

  •     24 
    17)4138
       34
        73
        68
         58

  • Divide 58 by 17 and place that answer (3) above the division bracket and to the right of the four.

  •     243
    17)4138
       34
        73
        68
         58

  • Multiply the 3 of the quotient by the divisor (17) to get 51 and place this below the 58 under the dividend. Subtract 51 from 58 to give an answer of 7.

  •     243
    17)4138
       34
        73
        68
         58
         51
          7

  • There are no more digits in the dividend to bring down so the 7 is a remainder. The final answer could be written in several ways.
    243 remainder 7 or sometimes 243r7
    or as a mixed number 243  7/17

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