Find the sum of all the numbers greater than 10000 formed with the digits 0, 2, 4, 6 and 8. Digits are not repeated.
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Since, this may go really messy, I would solve this question step by step, So please bear with me!
For Ones place:
When an 8 is placed, the total amount of numbers formed = 3 × 3 × 2 × 1 = 1 8
When a 6 is placed, the total amount of numbers formed = 3 × 3 × 2 × 1 = 1 8
When a 4 is placed, the total amount of numbers formed = 3 × 3 × 2 × 1 = 1 8
When a 2 is placed, the total amount of numbers formed = 3 × 3 × 2 × 1 = 1 8
When a 0 is placed, the total amount of numbers formed = 4 × 3 × 2 × 1 = 2 4
Sum at one's place = ( 8 + 6 + 4 + 2 ) 1 8 + ( 0 ) 2 4 = 2 0 × 1 8 --------- 1 .
This same pattern will be followed for the ten's, the hundred's and the thousand's place. So, using the same formula:
Sum at ten's place = ( ( 8 + 6 + 4 + 2 ) 1 8 + ( 0 ) 2 4 ) × 1 0 = 2 0 0 × 1 8 ----------- 2 .
Sum at hundred's place = ( ( 8 + 6 + 4 + 2 ) 1 8 + ( 0 ) 2 4 ) × 1 0 0 = 2 0 0 0 × 1 8 ----------- 3 .
Sum at thousand's place = ( ( 8 + 6 + 4 + 2 ) 1 8 + ( 0 ) 2 4 ) × 1 0 0 0 = 2 0 0 0 0 × 1 8 ----------- 4 .
Now for the ten thousand's place:
When an 8 is placed, the total amount of numbers formed = 4 × 3 × 2 × 1 = 2 4
When a 6 is placed, the total amount of numbers formed = 4 × 3 × 2 × 1 = 2 4
When a 4 is placed, the total amount of numbers formed = 4 × 3 × 2 × 1 = 2 4
When a 2 is placed, the total amount of numbers formed = 4 × 3 × 2 × 1 = 2 4
Sum at ten thousand's place = ( ( 8 + 6 + 4 + 2 ) × 2 4 ) × 1 0 0 0 0 = 2 0 0 0 0 × 2 4 ------------- 5 .
Total sum = 1 . + 2 . + 3 . + 4 . + 5 .
= 3 6 0 + 3 6 0 0 + 3 6 0 0 0 + 3 6 0 0 0 0 + 4 8 0 0 0 0 0
= 3 6 × ( 1 0 + 1 0 0 + 1 0 0 0 + 1 0 0 0 0 ) + 4 8 0 0 0 0 0
= 3 6 × ( 1 1 1 1 0 ) + 4 8 0 0 0 0 0
= 3 9 9 9 6 0 + 4 8 0 0 0 0 0
= 5 1 9 9 9 6 0
CHEERS!:)
YO!! I did it exactly the same way!
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Haha...Well done @shuvayan ghosh dastidar !!:D:D
De acordo com a permutação simples, teríamos 5 ! possibilidades de números distintos com 5 dígitos diferentes, porém um desses é 0 , que à esquerda não vale nada, logo o total passa a ser 4 ∗ 4 ∗ 3 ∗ 2 ∗ 1 = 9 6 números. Agora vem a parte mais chatinha, pois precisamos descobrir a soma dos mesmos.
Partindo das unidades, escolhemos qualquer algorismo para ser fixo a fim de teste, por exemplo o 2 :
? ? ? ? 2
Novamente relembrando, como 0 não pode ser o primeiro dígito, temos 3 ∗ 3 ∗ 2 ∗ 1 = 1 8 números que terminam em 2 . Assim, 1 8 ∗ 2 é a soma de todas as casas decimais de valor 2 .
Repetimos o procedimento para todos os outros dígitos, então temos que a soma de todas as casas decimais dos 96 números é:
1 8 ∗ 2 + 1 8 ∗ 4 + 1 8 ∗ 6 + 1 8 ∗ 8
ou
1 8 ( 2 + 4 + 6 + 8 ) = 3 6 0 = 3 6 ∗ 1 0
O procedimento para as demais casas dos números é bastante similar, apenas utilizamos a potência de 10 para ajustar o valor real da sua posição.
1 8 ∗ 2 0 ∗ 1 0 = 3 . 6 0 0 = 3 6 ∗ 1 0 2
1 8 ∗ 2 0 ∗ 1 0 2 = 3 6 . 0 0 0 = 3 6 ∗ 1 0 3
1 8 ∗ 2 0 ∗ 1 0 3 = 3 6 0 . 0 0 0 = 3 6 ∗ 1 0 4
Até agora já calculamos o valor de 1 8 ∗ 4 números, faltam os terminados em 0 .
Sendo esse o último dígito, teríamos mais números, pois desse modo garantíamos que ele não seria o primeiro, e assim teremos apenas números válidos para a condição de valor > 1 0 . 0 0 0 .
? ? ? ? 0
4 ∗ 3 ∗ 2 ∗ 1 = 2 4
Logo,
2 4 ∗ 2 0 ∗ 1 0 4 = 4 . 8 0 0 . 0 0 0
Agora somamos tudo
4 . 8 0 0 . 0 0 0 + 3 6 ∗ 1 1 . 1 1 0 = 5 . 1 9 9 . 9 6 0
:) Espero ter ajudado, abraços!
Python:
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Whenever I've seen a solution by you, why has it always been Python ?
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Because it's my favorite way to solve things. I use this site mainly to practice my programming. I'm not great at traditional mathematical thinking, so I get around that problem with Python.
I know it's not a good idea to use Python as a crutch, but I enjoy it. :D
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where can i learn python ????? cuz i want to
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@Vaibhav Prasad – Here you go:
Learn Python the Hard Way: http://learnpythonthehardway.org/book/
MIT's Introduction to Python: https://www.edx.org/course/introduction-computer-science-mitx-6-00-1x-0#.VNtP4np6jqA
MIT's Introduction to Algorithms: http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-006-introduction-to-algorithms-fall-2011/
The Python documentation is also very thorough: https://docs.python.org/2.7/
If you have any questions, don't hesisitate to ask:
brockrbrown@gmail.com
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@Brock Brown – whoa....ok. thanks a lot
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Sum of all numbers formed using digits 0 , 2 , 4 , 6 & 8 = ( 0 + 2 + 4 + 6 + 8 ) × ( 4 ! ) × ( 1 1 1 1 1 ) = 5 3 3 3 2 8 0
sum of all numbers formed by given digits which are less than 1 0 0 0 0 a l l 4 d i g i t n u m b e r s = ( 2 + 4 + 6 + 8 ) × ( 3 ! ) × ( 1 1 1 1 ) = 1 3 3 3 2 0
Hence required sum = ( 5 3 3 3 2 8 0 ) − ( 1 3 3 3 2 0 ) = 5 1 9 9 9 6 0