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#1 2012-10-16 05:32:09
- juan
- Guest
Sum of no.
(1) The sum of all no. that can be formed by using the digits
(2) Total no. of positive Integer solution of
(3) Total no. of positive Integer solution of
#2 2012-10-16 05:47:48
- anonimnystefy
- Real Member
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Re: Sum of no.
For (1): Must all the digits be used in making one number?
The limit operator is just an excuse for doing something you know you can't.
“It's the subject that nobody knows anything about that we can all talk about!” ― Richard Feynman
“A secret's worth depends on the people from whom it must be kept.” ― Carlos Ruiz Zafón
#3 2012-10-16 05:52:04
- bob bundy
- Moderator
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Re: Sum of no.
Q1. There are 7 digits. Pretend they are all different, a,b,c,d,e,f,g say.
Find all the possibilities:
a, ab, abc, .......fg, g
Now allow for the repeats by dividing (eg if all 4s then divide by 4!)
Might be easier to count by taking all the 4s; then only three 4s then only two etc.
Q2. No number can be over 10 or under 1.
So 10 + 1 + 1
9 + 2 + 1
9 + 1 + 2
etc. It's not so bad to continue like this, is it?
That should show you a generating technique which will make Q3 easy.
Bob
You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei
#4 2012-10-16 05:56:43
- anonimnystefy
- Real Member
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Re: Sum of no.
bob bundy wrote:
Q1. There are 7 digits. Pretend they are all different, a,b,c,d,e,f,g say.
Find all the possibilities:
a, ab, abc, .......fg, g
Now allow for the repeats by dividing (eg if all 4s then divide by 4!)
Might be easier to count by taking all the 4s; then only three 4s then only two etc.
Q2. No number can be over 10 or under 1.
So 10 + 1 + 1
9 + 2 + 1
9 + 1 + 2
etc. It's not so bad to continue like this, is it?
That should show you a generating technique which will make Q3 easy.
Bob
We don't need the number of those kind of nos in tthe first problem. And in the second problem, the numbers an also take on a negative value...
The limit operator is just an excuse for doing something you know you can't.
“It's the subject that nobody knows anything about that we can all talk about!” ― Richard Feynman
“A secret's worth depends on the people from whom it must be kept.” ― Carlos Ruiz Zafón
#5 2012-10-16 12:29:03
- bobbym
- Administrator
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Re: Sum of no.
Hi juan;
For 1)
I am getting 399999960. I am assuming you want to use all seven numbers to form a seven digit number.
For 2) I am getting 578.
For 3) I am getting 4672.
In mathematics, you don't understand things. You just get used to them.
90% of mathematicians do not understand 90% of currently published mathematics.
I am willing to wager that over 75% of the new words that appeared were nothing more than spelling errors that caught on.