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25 votes
25 votes
Can someone teach me How to do long division properly?

User Wodesuck
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1 Answer

11 votes
11 votes

Explanation:

"properly" is very vague.

as your can imagine, particularly in math, where many things are commutative or have other degrees of freedom what do when in what sequence, you will find particularly for the little techniques many different approaches. and most of them are correct.

particularly today I keep scratching my head about what i think is immensely complicated but teachers swear they are helping the students.

anyway, this is how I do divisions by using an example :

73496 ÷ 17

the "window" I use to look at the first number is a long as the second number. in this case 2 digits.

step 1a :

as mentioned, we look at the 2 left most digits (73) and see how often 17 fits inside that as a whole :

73 ÷ 17 = 4

4×17 = 68, so we have a remainder of 73-68 = 5.

I write it like this :

73|496 ÷ 17 = 4

05 (4×7 = 28 and 5 is then 33, carry over 3,

4×1 = 4 plus carry 3 = 7, 0 difference)

step 1b :

pull the next position down

734|96 ÷ 17 = 4

054

step 2a :

we look at the bottom number and divide this by 17.

54 ÷ 17 = 3 and a remainder of 3.

734|96 ÷ 17 = 43

054

03 (3×7 = 21 and 3 is then 24, carry over 2,

3×1 = 3 plus carry 2 = 5, 0 difference)

step 2b :

pull the next position down

7349|6 ÷ 17 = 43

054

039

step 3a :

we look at the bottom number and divide this by 17.

39 ÷ 17 = 2 and a remainder of 5.

734|96 ÷ 17 = 432

054

039

05 (2×7 = 14 and 5 is then 19, carry over 1,

2×1 = 2 plus carry 1 = 3, 0 difference)

step 3b :

pull the next position down

73496| ÷ 17 = 432

054

039

056

step 4a :

we look at the bottom number and divide this by 17.

56 ÷ 17 = 3 and a remainder of 5.

73496| ÷ 17 = 4323

054

039

056

05 (3×7 = 21 and 5 is then 26, carry over 2,

3×1 = 3 plus carry 2 = 5, 0 difference)

step 4b :

pull the next position down. but we have reached the last position before the decimal point. from that moment on we create result numbers after the decimal point.

and because the left number did not have any explicit digits after the decimal point, all the numbers we are pulling down now are 0.

73496.0| ÷ 17 = 4323.

054

039

056

050

step 5a :

we look at the bottom number and divide this by 17.

50 ÷ 17 = 2 and a remainder of 16.

73496.0| ÷ 17 = 4323.2

054

039

056

050

16 (2×7 = 14 and 6 is then 20, carry over 2,

2×1 = 2 plus carry 2 = 4, 1 difference)

step 5b :

pull the next position down. because the left number did not have any explicit digits after the decimal point, all the numbers we are pulling down now are 0.

73496.00| ÷ 17 = 4323.2

054

039

056

050

160

step 6a :

we look at the bottom number and divide this by 17.

160 ÷ 17 = 9 and a remainder of 7.

73496.00| ÷ 17 = 4323.29

054

039

056

050

160

07 (2×7 = 14 and 6 is then 20, carry over 2,

2×1 = 2 plus carry 2 = 4, 1 difference)

step 6b :

pull the next position down. because the left number did not have any explicit digits after the decimal point, all the numbers we are pulling down now are 0.

73496.000| ÷ 17 = 4323.29

054

039

056

050

160

070

step 7a :

we look at the bottom number and divide this by 17.

70 ÷ 17 = 4 and a remainder of 2.

73496.00| ÷ 17 = 4323.294

054

039

056

050

160

070

02 (4×7 = 28 and 2 is then 30, carry over 3,

4×1 = 4 plus carry 3 = 7, 0 difference)

step 7b :

pull the next position down. because the left number did not have any explicit digits after the decimal point, all the numbers we are pulling down now are 0.

73496.0000| ÷ 17 = 4323.294

054

039

056

050

160

070

020

and so on ...