Split $151$ cakes amongst $3$ people
$begingroup$
$151$ cakes shall be split amongst $3$ people under the condition that no one must have more than $75$. How many combinations are possible?
The solution is $${binom {3+74-1}{3-1}}$$
which is exactly a combination with replacement.
I don't understand why the number of cakes can be reduced to $74$. There must be some kind of bijectivity between splitting $151$ cakes and the $74$ I don't see.
combinatorics
$endgroup$
add a comment |
$begingroup$
$151$ cakes shall be split amongst $3$ people under the condition that no one must have more than $75$. How many combinations are possible?
The solution is $${binom {3+74-1}{3-1}}$$
which is exactly a combination with replacement.
I don't understand why the number of cakes can be reduced to $74$. There must be some kind of bijectivity between splitting $151$ cakes and the $74$ I don't see.
combinatorics
$endgroup$
add a comment |
$begingroup$
$151$ cakes shall be split amongst $3$ people under the condition that no one must have more than $75$. How many combinations are possible?
The solution is $${binom {3+74-1}{3-1}}$$
which is exactly a combination with replacement.
I don't understand why the number of cakes can be reduced to $74$. There must be some kind of bijectivity between splitting $151$ cakes and the $74$ I don't see.
combinatorics
$endgroup$
$151$ cakes shall be split amongst $3$ people under the condition that no one must have more than $75$. How many combinations are possible?
The solution is $${binom {3+74-1}{3-1}}$$
which is exactly a combination with replacement.
I don't understand why the number of cakes can be reduced to $74$. There must be some kind of bijectivity between splitting $151$ cakes and the $74$ I don't see.
combinatorics
combinatorics
edited 5 hours ago
Asaf Karagila♦
306k33437768
306k33437768
asked 6 hours ago
EpsilonDeltaEpsilonDelta
6921615
6921615
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2 Answers
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$begingroup$
The solutions of the system :
$$
x_1 + x_2 + x_3 = 151 : 0 leq x_1,x_2,x_3 leq 75 \
$$
is in one-one correspondence with the solutions of the system :
$$
(75 - x_1) + (75 - x_2) + (75 - x_3) = 3 times 75 - 151 : 0 leq x_1,x_2,x_3 leq 75
$$
Which after the change of variable $y_i = 75-x_i$ becomes (since $color{blue}{75times3 - 151 = 74}$):
$$
y_1+y_2+y_3 = 74 : 0 leq y_1,y_2,y_3 leq 75
$$
which by non-negativity has the same solutions as :
$$
y_1+y_2+y_3 = 74 : 0 leq y_i forall i
$$
Now, play the stars-and-bars game to find the number of solutions of this equation.
$endgroup$
add a comment |
$begingroup$
The number of possibilities is like choosing two numbers from 75 (with replacement). Hence it is $$left(!!!binom{75}{2}!!!right)=binom{75+2-1}{2}=binom{74+3-1}{3-1}$$
This requires some explanation: There is only one way of combining the two numbers to give three numbers less than 75. For example, if you choose 21 and 12, then think of 75 as being split into 21+54 and 12+63; the only way to combine them to give three acceptable numbers is as 54+33+63. In general, one must combine the two numbers that are smaller than half 75.
$endgroup$
add a comment |
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2 Answers
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2 Answers
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$begingroup$
The solutions of the system :
$$
x_1 + x_2 + x_3 = 151 : 0 leq x_1,x_2,x_3 leq 75 \
$$
is in one-one correspondence with the solutions of the system :
$$
(75 - x_1) + (75 - x_2) + (75 - x_3) = 3 times 75 - 151 : 0 leq x_1,x_2,x_3 leq 75
$$
Which after the change of variable $y_i = 75-x_i$ becomes (since $color{blue}{75times3 - 151 = 74}$):
$$
y_1+y_2+y_3 = 74 : 0 leq y_1,y_2,y_3 leq 75
$$
which by non-negativity has the same solutions as :
$$
y_1+y_2+y_3 = 74 : 0 leq y_i forall i
$$
Now, play the stars-and-bars game to find the number of solutions of this equation.
$endgroup$
add a comment |
$begingroup$
The solutions of the system :
$$
x_1 + x_2 + x_3 = 151 : 0 leq x_1,x_2,x_3 leq 75 \
$$
is in one-one correspondence with the solutions of the system :
$$
(75 - x_1) + (75 - x_2) + (75 - x_3) = 3 times 75 - 151 : 0 leq x_1,x_2,x_3 leq 75
$$
Which after the change of variable $y_i = 75-x_i$ becomes (since $color{blue}{75times3 - 151 = 74}$):
$$
y_1+y_2+y_3 = 74 : 0 leq y_1,y_2,y_3 leq 75
$$
which by non-negativity has the same solutions as :
$$
y_1+y_2+y_3 = 74 : 0 leq y_i forall i
$$
Now, play the stars-and-bars game to find the number of solutions of this equation.
$endgroup$
add a comment |
$begingroup$
The solutions of the system :
$$
x_1 + x_2 + x_3 = 151 : 0 leq x_1,x_2,x_3 leq 75 \
$$
is in one-one correspondence with the solutions of the system :
$$
(75 - x_1) + (75 - x_2) + (75 - x_3) = 3 times 75 - 151 : 0 leq x_1,x_2,x_3 leq 75
$$
Which after the change of variable $y_i = 75-x_i$ becomes (since $color{blue}{75times3 - 151 = 74}$):
$$
y_1+y_2+y_3 = 74 : 0 leq y_1,y_2,y_3 leq 75
$$
which by non-negativity has the same solutions as :
$$
y_1+y_2+y_3 = 74 : 0 leq y_i forall i
$$
Now, play the stars-and-bars game to find the number of solutions of this equation.
$endgroup$
The solutions of the system :
$$
x_1 + x_2 + x_3 = 151 : 0 leq x_1,x_2,x_3 leq 75 \
$$
is in one-one correspondence with the solutions of the system :
$$
(75 - x_1) + (75 - x_2) + (75 - x_3) = 3 times 75 - 151 : 0 leq x_1,x_2,x_3 leq 75
$$
Which after the change of variable $y_i = 75-x_i$ becomes (since $color{blue}{75times3 - 151 = 74}$):
$$
y_1+y_2+y_3 = 74 : 0 leq y_1,y_2,y_3 leq 75
$$
which by non-negativity has the same solutions as :
$$
y_1+y_2+y_3 = 74 : 0 leq y_i forall i
$$
Now, play the stars-and-bars game to find the number of solutions of this equation.
answered 6 hours ago
астон вілла олоф мэллбэргастон вілла олоф мэллбэрг
39.1k33477
39.1k33477
add a comment |
add a comment |
$begingroup$
The number of possibilities is like choosing two numbers from 75 (with replacement). Hence it is $$left(!!!binom{75}{2}!!!right)=binom{75+2-1}{2}=binom{74+3-1}{3-1}$$
This requires some explanation: There is only one way of combining the two numbers to give three numbers less than 75. For example, if you choose 21 and 12, then think of 75 as being split into 21+54 and 12+63; the only way to combine them to give three acceptable numbers is as 54+33+63. In general, one must combine the two numbers that are smaller than half 75.
$endgroup$
add a comment |
$begingroup$
The number of possibilities is like choosing two numbers from 75 (with replacement). Hence it is $$left(!!!binom{75}{2}!!!right)=binom{75+2-1}{2}=binom{74+3-1}{3-1}$$
This requires some explanation: There is only one way of combining the two numbers to give three numbers less than 75. For example, if you choose 21 and 12, then think of 75 as being split into 21+54 and 12+63; the only way to combine them to give three acceptable numbers is as 54+33+63. In general, one must combine the two numbers that are smaller than half 75.
$endgroup$
add a comment |
$begingroup$
The number of possibilities is like choosing two numbers from 75 (with replacement). Hence it is $$left(!!!binom{75}{2}!!!right)=binom{75+2-1}{2}=binom{74+3-1}{3-1}$$
This requires some explanation: There is only one way of combining the two numbers to give three numbers less than 75. For example, if you choose 21 and 12, then think of 75 as being split into 21+54 and 12+63; the only way to combine them to give three acceptable numbers is as 54+33+63. In general, one must combine the two numbers that are smaller than half 75.
$endgroup$
The number of possibilities is like choosing two numbers from 75 (with replacement). Hence it is $$left(!!!binom{75}{2}!!!right)=binom{75+2-1}{2}=binom{74+3-1}{3-1}$$
This requires some explanation: There is only one way of combining the two numbers to give three numbers less than 75. For example, if you choose 21 and 12, then think of 75 as being split into 21+54 and 12+63; the only way to combine them to give three acceptable numbers is as 54+33+63. In general, one must combine the two numbers that are smaller than half 75.
edited 2 hours ago
answered 6 hours ago
ChrystomathChrystomath
1,343512
1,343512
add a comment |
add a comment |
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