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hi PeterKing,
Here is my formula:
For the 1st digit, you have only 3 choices(3, 4 & 5). "0" cannot be the first digit of any natural no.
For the 2nd digit, you can choose between all the numbers other than the one you picked for 1st digit, so you got 4 choices.
Similar case, for the 3rd digit, you remains 3 choices.
For the fouth digit, you have only 2 choices.
While the fifth digit, you got only 1 no. remained.
Therefore, the possible combination is equal to 3 x 4 x 3 x 2 x 1 or 72. But be reminded that there are 2 "0" in these combinations which generate the same value with no different. So, we should divide the 72 by 2. That is 36.
Or, we can simply use the formula : (3x4x3x2x1)/2=36. |
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