Monday, August 11, 2008

Product of a single digit number with 9

This algorithm is useful for kids that are lazy enough to memorize the multiplication table of 9.

The algorithm works like this:

Suppose you want a product of n and 9, you can do

  1. n - 1

  2. 10 -n

  3. The answer is (n-1) as the first digit and (10 - n) as the second digit.


Example:

4 x 9 =36

First digit: 4 - 1 = 3

Second digit: 10 - 4 = 6

Note: This trick only works on multiplication of any single digit number with 9.

7 comments :

  1. perghhhh something new aku belajar hari ni ni. hehe :mrgreen:

    tak pasang shoutbox ke eh ?

    ReplyDelete
  2. Anak2 sy ada satu cara mudah waktu kita 'tolak' nombor kecil di atas dengan nombot 'besar' di bawah

    contoh

    42
    - 19

    Proses dia kalau angka di bawah lagi besar, tolak dari bawah = 9-2 = 7
    otometik dia akan tulis =3


    4 tinggal 3, jadi senang untuk tolak 1.

    Bila guna mcm ni. dia tak perlu bayangkankan dalam otak angka belas2...contoh tadi 4 di potong jadi 3. 2 tambah 10 akan jadi 12. Dari 12 baru di tolak 9.

    Tapi sistem ini hanya berhasil jika kita hafal formula ini

    Kalau

    1 perlu tulis 9
    2 perlu tulis 8
    3 perlu tulis 7
    4 perlu tulis 6
    5 tetap dgn 5

    ReplyDelete
  3. atok saya ajar cara ni..

    listkan no 0-9 (0 1 2 3 4 5 6 7 8 9)
    pastu listkan skali lagi tapi diterbalikkan (9 8 7 6 5 4 3 2 1 0)
    so dia jadi macam ni...
    0 9
    1 8
    2 7
    3 6
    4 5
    5 4
    6 3
    7 2
    8 1
    9 0

    Adilas last blog post..Old Mates II

    ReplyDelete
  4. Adila: Nice. However, your technique and neither mine could solve a multiplication of 2 digits number and a nine.

    ReplyDelete
  5. apasal tak guna calculator jer? lagi senang.. :idea:

    ReplyDelete