Number of positive unequal integer solution
$begingroup$
Number of positive unequal integer solution of
$x_{1}+x_{2}+x_{3}+x_{4}=20,$ is
Try: Total number of positive integer solution is
$displaystyle binom{20-1}{4-1}=binom{19}{3}.$ (Using star and bar method)
Now for unequal integer solution, First we will find Total positive integer solution.
And subtract the cases where any three are equal and any two are equal and all are equal.
So Total number of positive integer solution is
$displaystyle binom{20-1}{4-1}=binom{19}{3}.$ (Using star and bar method)
And number of positive integer solution in which all are equal i. e $x_{1}=x_{2}=x_{3}=x_{4}.$ Which is only one quadraplets.
Now if all any three are equal i. e $x_{1}=x_{2}=x_{3}$. Then $3x_{1}+x_{4}=20.$ we have $6times 4=24.$
If any two are equal. i. e $x_{1}=x_{2}.$
Then $2x_{1}+x_{2}+x_{3}=20.$ So we have $6times displaystyle sum^{9}_{k=1}binom{19-2k}{1}=6sum^{9}_{k=1}(19-k)=126times6=756.$
So Total number of positive nequal inteher solution $$binom{19}{3}-1-24-756=969-781=$$
But answer given as $552.$
Could some help me How to solve it, Thanks
combinatorics
$endgroup$
add a comment |
$begingroup$
Number of positive unequal integer solution of
$x_{1}+x_{2}+x_{3}+x_{4}=20,$ is
Try: Total number of positive integer solution is
$displaystyle binom{20-1}{4-1}=binom{19}{3}.$ (Using star and bar method)
Now for unequal integer solution, First we will find Total positive integer solution.
And subtract the cases where any three are equal and any two are equal and all are equal.
So Total number of positive integer solution is
$displaystyle binom{20-1}{4-1}=binom{19}{3}.$ (Using star and bar method)
And number of positive integer solution in which all are equal i. e $x_{1}=x_{2}=x_{3}=x_{4}.$ Which is only one quadraplets.
Now if all any three are equal i. e $x_{1}=x_{2}=x_{3}$. Then $3x_{1}+x_{4}=20.$ we have $6times 4=24.$
If any two are equal. i. e $x_{1}=x_{2}.$
Then $2x_{1}+x_{2}+x_{3}=20.$ So we have $6times displaystyle sum^{9}_{k=1}binom{19-2k}{1}=6sum^{9}_{k=1}(19-k)=126times6=756.$
So Total number of positive nequal inteher solution $$binom{19}{3}-1-24-756=969-781=$$
But answer given as $552.$
Could some help me How to solve it, Thanks
combinatorics
$endgroup$
2
$begingroup$
When counting the solutions where any 3 variables are equal, you included the solution with all 4 equal. In fact you included it 4 times. – I suppose you made a similar mistake for the solutions with 2 variables being equal.
$endgroup$
– Christoph
Dec 7 '18 at 7:24
$begingroup$
Are you looking for solutions where none of the $x_i$'s are equal or the ones where not all four are equal?
$endgroup$
– Anurag A
Dec 7 '18 at 8:03
add a comment |
$begingroup$
Number of positive unequal integer solution of
$x_{1}+x_{2}+x_{3}+x_{4}=20,$ is
Try: Total number of positive integer solution is
$displaystyle binom{20-1}{4-1}=binom{19}{3}.$ (Using star and bar method)
Now for unequal integer solution, First we will find Total positive integer solution.
And subtract the cases where any three are equal and any two are equal and all are equal.
So Total number of positive integer solution is
$displaystyle binom{20-1}{4-1}=binom{19}{3}.$ (Using star and bar method)
And number of positive integer solution in which all are equal i. e $x_{1}=x_{2}=x_{3}=x_{4}.$ Which is only one quadraplets.
Now if all any three are equal i. e $x_{1}=x_{2}=x_{3}$. Then $3x_{1}+x_{4}=20.$ we have $6times 4=24.$
If any two are equal. i. e $x_{1}=x_{2}.$
Then $2x_{1}+x_{2}+x_{3}=20.$ So we have $6times displaystyle sum^{9}_{k=1}binom{19-2k}{1}=6sum^{9}_{k=1}(19-k)=126times6=756.$
So Total number of positive nequal inteher solution $$binom{19}{3}-1-24-756=969-781=$$
But answer given as $552.$
Could some help me How to solve it, Thanks
combinatorics
$endgroup$
Number of positive unequal integer solution of
$x_{1}+x_{2}+x_{3}+x_{4}=20,$ is
Try: Total number of positive integer solution is
$displaystyle binom{20-1}{4-1}=binom{19}{3}.$ (Using star and bar method)
Now for unequal integer solution, First we will find Total positive integer solution.
And subtract the cases where any three are equal and any two are equal and all are equal.
So Total number of positive integer solution is
$displaystyle binom{20-1}{4-1}=binom{19}{3}.$ (Using star and bar method)
And number of positive integer solution in which all are equal i. e $x_{1}=x_{2}=x_{3}=x_{4}.$ Which is only one quadraplets.
Now if all any three are equal i. e $x_{1}=x_{2}=x_{3}$. Then $3x_{1}+x_{4}=20.$ we have $6times 4=24.$
If any two are equal. i. e $x_{1}=x_{2}.$
Then $2x_{1}+x_{2}+x_{3}=20.$ So we have $6times displaystyle sum^{9}_{k=1}binom{19-2k}{1}=6sum^{9}_{k=1}(19-k)=126times6=756.$
So Total number of positive nequal inteher solution $$binom{19}{3}-1-24-756=969-781=$$
But answer given as $552.$
Could some help me How to solve it, Thanks
combinatorics
combinatorics
edited Dec 7 '18 at 7:46
DXT
asked Dec 7 '18 at 7:11
DXTDXT
5,6662630
5,6662630
2
$begingroup$
When counting the solutions where any 3 variables are equal, you included the solution with all 4 equal. In fact you included it 4 times. – I suppose you made a similar mistake for the solutions with 2 variables being equal.
$endgroup$
– Christoph
Dec 7 '18 at 7:24
$begingroup$
Are you looking for solutions where none of the $x_i$'s are equal or the ones where not all four are equal?
$endgroup$
– Anurag A
Dec 7 '18 at 8:03
add a comment |
2
$begingroup$
When counting the solutions where any 3 variables are equal, you included the solution with all 4 equal. In fact you included it 4 times. – I suppose you made a similar mistake for the solutions with 2 variables being equal.
$endgroup$
– Christoph
Dec 7 '18 at 7:24
$begingroup$
Are you looking for solutions where none of the $x_i$'s are equal or the ones where not all four are equal?
$endgroup$
– Anurag A
Dec 7 '18 at 8:03
2
2
$begingroup$
When counting the solutions where any 3 variables are equal, you included the solution with all 4 equal. In fact you included it 4 times. – I suppose you made a similar mistake for the solutions with 2 variables being equal.
$endgroup$
– Christoph
Dec 7 '18 at 7:24
$begingroup$
When counting the solutions where any 3 variables are equal, you included the solution with all 4 equal. In fact you included it 4 times. – I suppose you made a similar mistake for the solutions with 2 variables being equal.
$endgroup$
– Christoph
Dec 7 '18 at 7:24
$begingroup$
Are you looking for solutions where none of the $x_i$'s are equal or the ones where not all four are equal?
$endgroup$
– Anurag A
Dec 7 '18 at 8:03
$begingroup$
Are you looking for solutions where none of the $x_i$'s are equal or the ones where not all four are equal?
$endgroup$
– Anurag A
Dec 7 '18 at 8:03
add a comment |
1 Answer
1
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$begingroup$
Counting the positive integer solutions of $x_1+x_2+x_3+x_4=20$ with unequal parts, we may assume $x_1<x_2<x_3<x_4$ and multiply by $4!$ in the end.
Now letting $y_i = x_i - i$ for $i=1,2,3,4$ this translates to counting quadruplets $(y_1,y_2,y_3,y_4)$ of non-negative integers with $y_1le y_2le y_3le y_4$ and $y_1+y_2+y_3+y_4=10$. Hence, we are counting partitions of $10$ with at most $4$ parts. These are $23$:
begin{align*}
10 &= 10 \
&= 9+1 = 8+2 = 7+3 = 6+4 = 5+5 \
&= 8+1+1 = 7+2+1 = 6+3+1 = 6+2+2 \
&= 5+4+1 = 5+3+2 = 4+4+2 = 4+3+3 \
&= 7+1+1+1 \&= 6+2+1+1 \&= 5+3+1+1 = 5+2+2+1 \
&= 4+4+1+1 = 4+3+2+1 = 4+2+2+2 \
&= 3+3+3+1 = 3+3+2+2.
end{align*}
Hence, there are $23cdot 4!=552$ solutions to your problem.
You could also go one more step and let $z_1=y_1$, $z_i=y_i-y_{i-1}$ for $i=2,3,4$ to translate this to counting the non-negative integer solutions of $4z_1+3z_2+2z_3+z_4=10$. (This amounts to conjugating the partitions and count those with parts of size at most $4$)
$endgroup$
add a comment |
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$begingroup$
Counting the positive integer solutions of $x_1+x_2+x_3+x_4=20$ with unequal parts, we may assume $x_1<x_2<x_3<x_4$ and multiply by $4!$ in the end.
Now letting $y_i = x_i - i$ for $i=1,2,3,4$ this translates to counting quadruplets $(y_1,y_2,y_3,y_4)$ of non-negative integers with $y_1le y_2le y_3le y_4$ and $y_1+y_2+y_3+y_4=10$. Hence, we are counting partitions of $10$ with at most $4$ parts. These are $23$:
begin{align*}
10 &= 10 \
&= 9+1 = 8+2 = 7+3 = 6+4 = 5+5 \
&= 8+1+1 = 7+2+1 = 6+3+1 = 6+2+2 \
&= 5+4+1 = 5+3+2 = 4+4+2 = 4+3+3 \
&= 7+1+1+1 \&= 6+2+1+1 \&= 5+3+1+1 = 5+2+2+1 \
&= 4+4+1+1 = 4+3+2+1 = 4+2+2+2 \
&= 3+3+3+1 = 3+3+2+2.
end{align*}
Hence, there are $23cdot 4!=552$ solutions to your problem.
You could also go one more step and let $z_1=y_1$, $z_i=y_i-y_{i-1}$ for $i=2,3,4$ to translate this to counting the non-negative integer solutions of $4z_1+3z_2+2z_3+z_4=10$. (This amounts to conjugating the partitions and count those with parts of size at most $4$)
$endgroup$
add a comment |
$begingroup$
Counting the positive integer solutions of $x_1+x_2+x_3+x_4=20$ with unequal parts, we may assume $x_1<x_2<x_3<x_4$ and multiply by $4!$ in the end.
Now letting $y_i = x_i - i$ for $i=1,2,3,4$ this translates to counting quadruplets $(y_1,y_2,y_3,y_4)$ of non-negative integers with $y_1le y_2le y_3le y_4$ and $y_1+y_2+y_3+y_4=10$. Hence, we are counting partitions of $10$ with at most $4$ parts. These are $23$:
begin{align*}
10 &= 10 \
&= 9+1 = 8+2 = 7+3 = 6+4 = 5+5 \
&= 8+1+1 = 7+2+1 = 6+3+1 = 6+2+2 \
&= 5+4+1 = 5+3+2 = 4+4+2 = 4+3+3 \
&= 7+1+1+1 \&= 6+2+1+1 \&= 5+3+1+1 = 5+2+2+1 \
&= 4+4+1+1 = 4+3+2+1 = 4+2+2+2 \
&= 3+3+3+1 = 3+3+2+2.
end{align*}
Hence, there are $23cdot 4!=552$ solutions to your problem.
You could also go one more step and let $z_1=y_1$, $z_i=y_i-y_{i-1}$ for $i=2,3,4$ to translate this to counting the non-negative integer solutions of $4z_1+3z_2+2z_3+z_4=10$. (This amounts to conjugating the partitions and count those with parts of size at most $4$)
$endgroup$
add a comment |
$begingroup$
Counting the positive integer solutions of $x_1+x_2+x_3+x_4=20$ with unequal parts, we may assume $x_1<x_2<x_3<x_4$ and multiply by $4!$ in the end.
Now letting $y_i = x_i - i$ for $i=1,2,3,4$ this translates to counting quadruplets $(y_1,y_2,y_3,y_4)$ of non-negative integers with $y_1le y_2le y_3le y_4$ and $y_1+y_2+y_3+y_4=10$. Hence, we are counting partitions of $10$ with at most $4$ parts. These are $23$:
begin{align*}
10 &= 10 \
&= 9+1 = 8+2 = 7+3 = 6+4 = 5+5 \
&= 8+1+1 = 7+2+1 = 6+3+1 = 6+2+2 \
&= 5+4+1 = 5+3+2 = 4+4+2 = 4+3+3 \
&= 7+1+1+1 \&= 6+2+1+1 \&= 5+3+1+1 = 5+2+2+1 \
&= 4+4+1+1 = 4+3+2+1 = 4+2+2+2 \
&= 3+3+3+1 = 3+3+2+2.
end{align*}
Hence, there are $23cdot 4!=552$ solutions to your problem.
You could also go one more step and let $z_1=y_1$, $z_i=y_i-y_{i-1}$ for $i=2,3,4$ to translate this to counting the non-negative integer solutions of $4z_1+3z_2+2z_3+z_4=10$. (This amounts to conjugating the partitions and count those with parts of size at most $4$)
$endgroup$
Counting the positive integer solutions of $x_1+x_2+x_3+x_4=20$ with unequal parts, we may assume $x_1<x_2<x_3<x_4$ and multiply by $4!$ in the end.
Now letting $y_i = x_i - i$ for $i=1,2,3,4$ this translates to counting quadruplets $(y_1,y_2,y_3,y_4)$ of non-negative integers with $y_1le y_2le y_3le y_4$ and $y_1+y_2+y_3+y_4=10$. Hence, we are counting partitions of $10$ with at most $4$ parts. These are $23$:
begin{align*}
10 &= 10 \
&= 9+1 = 8+2 = 7+3 = 6+4 = 5+5 \
&= 8+1+1 = 7+2+1 = 6+3+1 = 6+2+2 \
&= 5+4+1 = 5+3+2 = 4+4+2 = 4+3+3 \
&= 7+1+1+1 \&= 6+2+1+1 \&= 5+3+1+1 = 5+2+2+1 \
&= 4+4+1+1 = 4+3+2+1 = 4+2+2+2 \
&= 3+3+3+1 = 3+3+2+2.
end{align*}
Hence, there are $23cdot 4!=552$ solutions to your problem.
You could also go one more step and let $z_1=y_1$, $z_i=y_i-y_{i-1}$ for $i=2,3,4$ to translate this to counting the non-negative integer solutions of $4z_1+3z_2+2z_3+z_4=10$. (This amounts to conjugating the partitions and count those with parts of size at most $4$)
edited Dec 7 '18 at 8:16
answered Dec 7 '18 at 8:07
ChristophChristoph
11.9k1642
11.9k1642
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2
$begingroup$
When counting the solutions where any 3 variables are equal, you included the solution with all 4 equal. In fact you included it 4 times. – I suppose you made a similar mistake for the solutions with 2 variables being equal.
$endgroup$
– Christoph
Dec 7 '18 at 7:24
$begingroup$
Are you looking for solutions where none of the $x_i$'s are equal or the ones where not all four are equal?
$endgroup$
– Anurag A
Dec 7 '18 at 8:03