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 #4
avatar+26364 
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Jul 24, 2018
 #1
avatar
+1

Partitions of 12 =P(12) =77

COUNT THEM!

 

12 = 12
11 + 1 = 12
10 + 2 = 12
10 + 1 + 1 = 12
9 + 3 = 12
9 + 2 + 1 = 12
9 + 1 + 1 + 1 = 12
8 + 4 = 12
8 + 3 + 1 = 12
8 + 2 + 2 = 12
8 + 2 + 1 + 1 = 12
8 + 1 + 1 + 1 + 1 = 12
7 + 5 = 12
7 + 4 + 1 = 12
7 + 3 + 2 = 12
7 + 3 + 1 + 1 = 12
7 + 2 + 2 + 1 = 12
7 + 2 + 1 + 1 + 1 = 12
7 + 1 + 1 + 1 + 1 + 1 = 12
6 + 6 = 12
6 + 5 + 1 = 12
6 + 4 + 2 = 12
6 + 4 + 1 + 1 = 12
6 + 3 + 3 = 12
6 + 3 + 2 + 1 = 12
6 + 3 + 1 + 1 + 1 = 12
6 + 2 + 2 + 2 = 12
6 + 2 + 2 + 1 + 1 = 12
6 + 2 + 1 + 1 + 1 + 1 = 12
6 + 1 + 1 + 1 + 1 + 1 + 1 = 12
5 + 5 + 2 = 12
5 + 5 + 1 + 1 = 12
5 + 4 + 3 = 12
5 + 4 + 2 + 1 = 12
5 + 4 + 1 + 1 + 1 = 12
5 + 3 + 3 + 1 = 12
5 + 3 + 2 + 2 = 12
5 + 3 + 2 + 1 + 1 = 12
5 + 3 + 1 + 1 + 1 + 1 = 12
5 + 2 + 2 + 2 + 1 = 12
5 + 2 + 2 + 1 + 1 + 1 = 12
5 + 2 + 1 + 1 + 1 + 1 + 1 = 12
5 + 1 + 1 + 1 + 1 + 1 + 1 + 1 = 12
4 + 4 + 4 = 12
4 + 4 + 3 + 1 = 12
4 + 4 + 2 + 2 = 12
4 + 4 + 2 + 1 + 1 = 12
4 + 4 + 1 + 1 + 1 + 1 = 12
4 + 3 + 3 + 2 = 12
4 + 3 + 3 + 1 + 1 = 12
4 + 3 + 2 + 2 + 1 = 12
4 + 3 + 2 + 1 + 1 + 1 = 12
4 + 3 + 1 + 1 + 1 + 1 + 1 = 12
4 + 2 + 2 + 2 + 2 = 12
4 + 2 + 2 + 2 + 1 + 1 = 12
4 + 2 + 2 + 1 + 1 + 1 + 1 = 12
4 + 2 + 1 + 1 + 1 + 1 + 1 + 1 = 12
4 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 = 12
3 + 3 + 3 + 3 = 12
3 + 3 + 3 + 2 + 1 = 12
3 + 3 + 3 + 1 + 1 + 1 = 12
3 + 3 + 2 + 2 + 2 = 12
3 + 3 + 2 + 2 + 1 + 1 = 12
3 + 3 + 2 + 1 + 1 + 1 + 1 = 12
3 + 3 + 1 + 1 + 1 + 1 + 1 + 1 = 12
3 + 2 + 2 + 2 + 2 + 1 = 12
3 + 2 + 2 + 2 + 1 + 1 + 1 = 12
3 + 2 + 2 + 1 + 1 + 1 + 1 + 1 = 12
3 + 2 + 1 + 1 + 1 + 1 + 1 + 1 + 1 = 12
3 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 = 12
2 + 2 + 2 + 2 + 2 + 2 = 12
2 + 2 + 2 + 2 + 2 + 1 + 1 = 12
2 + 2 + 2 + 2 + 1 + 1 + 1 + 1 = 12
2 + 2 + 2 + 1 + 1 + 1 + 1 + 1 + 1 = 12
2 + 2 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 = 12
2 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 = 12
1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 = 12

Jul 24, 2018
 #1
avatar+26364 
+1

A two-digit integer is written next to itself twice, forming a six-digit number.
If the resulting number is divisible by 6,
then how many possibilities are there for the original two-digit number?

 

The two-digit integer: ab
The six-digit number:  ababab

 

\(\text{Divisible by $6$: If it is divisible by $2$ and by $3$ } \\ \text{Divisible by $2$: So $b$ must be even! $b=\{0,2,4,6,8\} $} \\ \text{Divisible by $3$: Sum the digits. The result must be divisible by $3$,} \\ \text{ $\qquad a+b+a+b+a+b = 3a+3b$, so ababab is always divisible by $3$ } \)

 

\(\begin{array}{|l|r|r|r|r|} \hline &a & b & ab & ababab \\ \hline 1.& 1 & 0 & 10 & 101010 \\ 2.& 1 & 2 & 12 & 121212 \\ 3.& 1 & 4 & 14 & 141414 \\ 4.& 1 & 6 & 16 & 161616 \\ 5.& 1 & 8 & 18 & 181818 \\ \hline 6.& 2 & 0 & 20 & 202020 \\ 7.& 2 & 2 & 22 & 222222 \\ 8.& 2 & 4 & 24 & 242424 \\ 9.& 2 & 6 & 26 & 262626 \\ 10.& 2 & 8 & 28 & 282828 \\ \hline 11.& 3 & 0 & 30 & 303030 \\ 12.& 3 & 2 & 32 & 323232 \\ 13.& 3 & 4 & 34 & 343434 \\ 14.& 3 & 6 & 36 & 363636 \\ 15.& 3 & 8 & 38 & 383838 \\ \hline 16.& 4 & 0 & 40 & 404040 \\ 17.& 4 & 2 & 42 & 424242 \\ 18.& 4 & 4 & 44 & 444444 \\ 19.& 4 & 6 & 46 & 464646 \\ 20.& 4 & 8 & 48 & 484848 \\ \hline 21.& 5 & 0 & 50 & 505050 \\ 22.& 5 & 2 & 52 & 525252 \\ 23.& 5 & 4 & 54 & 545454 \\ 24.& 5 & 6 & 56 & 565656 \\ 25.& 5 & 8 & 58 & 585858 \\ \hline 26.& 6 & 0 & 60 & 606060 \\ 27.& 6 & 2 & 62 & 626262 \\ 28.& 6 & 4 & 64 & 646464 \\ 29.& 6 & 6 & 66 & 666666 \\ 30.& 6 & 8 & 68 & 686868 \\ \hline 31.& 7 & 0 & 70 & 707070 \\ 32.& 7 & 2 & 72 & 727272 \\ 33.& 7 & 4 & 74 & 747474 \\ 34.& 7 & 6 & 76 & 767676 \\ 35.& 7 & 8 & 78 & 787878 \\ \hline 36.& 8 & 0 & 80 & 808080 \\ 37.& 8 & 2 & 82 & 828282 \\ 38.& 8 & 4 & 84 & 848484 \\ 39.& 8 & 6 & 85 & 868686 \\ 40.& 8 & 8 & 88 & 888888 \\ \hline 41.& 9 & 0 & 90 & 909090 \\ 42.& 9 & 2 & 92 & 929292 \\ 43.& 9 & 4 & 94 & 949494 \\ 44.& 9 & 6 & 96 & 969696 \\ 45.& 9 & 8 & 98 & 989898 \\ \hline \end{array}\)

 

There are 45 possibilities for the original two-digit number.

 

laugh

Jul 24, 2018
 #5
avatar+2439 
+1

Hello Guest, 

 

You have been proactive in attempting to simplify the numerator, and you are continuing to make significant headway. However, there is a slight algebraic error lying somewhere in your simplification, but I cannot pinpoint where because of the lack of work provided. Computations like these require extreme perserverance and accuracy. Any small imperfection will result in an answer that is horribly askew. 

 

\(3(2x^2+9x-5)+(4x^2-1)(x-5)\) For now, I am worrying about the simplification of the numerator. Let's distribute the 3 into the trinomial.
\(6x^2+27x-15+(4x^2-1)(x-5)\) It is time to expand the product of two binomials. 
\(\textcolor{red}{6x^2}\textcolor{blue}{+27x}\textcolor{green}{-15}+4x^3\textcolor{red}{-20x^2}\textcolor{blue}{-x}\textcolor{green}{+5}\) Combine all like terms. I have utilized color coding to show which terms combine. 
\(\)\(4x^3-14x^2+26x-10\)  
   

 

After this algebra, we are left with \(\frac{4x^3-14x^2+26x-10}{(x+5)(x-5)(2x-1)}\). Notice the discrepancies and try and locate the mistake. 

 

From here, you must factor the numerator and determine whether or not any of the factors of \(4x^3-14x^2+26x-10\) match those of the denominator. Factoring by grouping does not appear to be a valid option here, so you will most likely have to resort to methods such as the rational root theorem and the Descartes' Rules of Signs. To start, though, notice how each term is even, so one can factor out a 2 from every term. 

 

Good luck! 

Jul 24, 2018

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