Division by 5

Often, instead of dividing by 5, it is more convenient to multiply first by 2 and then divide the result by 10. For example,

1375/5 = 2750/10 = 275.

Another examples:

7205/5 = 14410/10 = 1441.

And a third one

980/5 = 1960/10 = 196.

(So multiplication by 2 can speed up division by 5 (and vice versa, of course.) There are simple ways to double natural numbers.)

The latter example suggests another way of dividing by 5: the order of the two tasks "multiply by 2" and "divide by 10" could be reversed if the number ends with 0. In this case, it is as easy to divide by 10 first:

980/5 = 98×2 = 196.


Related material
Read more...

  • Multiplication by 9, 99, 999, (Multiply + Subtract) etc.
  • Squaring 2-Digit Numbers
  • Multiplication by 2
  • Multiplication by 5
  • Multiplication by 9, 99, 999, etc. (Something Special)
  • Product of 10a + b and 10a + c where b + c = 10
  • Product of numbers close to 100
  • Product of two one-digit numbers greater than 5
  • Product of 2-digit numbers
  • Squaring Numbers in Range 26-50
  • Squaring Numbers in Range 51-100
  • Squares of Numbers That End in 5
  • Squares Can Be Computed Squentially
  • How to Compute Fast Any Square
  • Adding a Long List of Numbers
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