Solutions of the Equation... (Awesome)

Algebra Level 4

Find the number of positive integral solutions of x + 2 y + 3 z = 100. x + 2y + 3z = 100.

736 636 684 784

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3 solutions

Manit Kapoor
Dec 25, 2014

Range of x,y and z

99 >= x >= 1

48 >= y >= 1

32 >= z >= 1

the system contains one equation and 3 variables we have to take two values arbitrary (y and z i have taken)

when y=1

         z can be 1,2,3....32

when y=2

         z can be 1,2,3....31

when y=3

         z can be 1,2,3....31

and so it goes on till

when y=47

         z can be 1 only

when y=48

         z can be 1 only

Solutions=32+31+31+30+29+29+.....+2+1+1

=2(1+3+5+..+31)+(2 + 4+6+...32)

=512+272=784

nice and easy solution

Mardokay Mosazghi - 6 years, 5 months ago

awesome solution !!

ฟลุค เบะ - 6 years, 2 months ago
Pratik Shastri
Dec 24, 2014

Hint : You would look for the coefficient of x 94 x^{94} in the taylor expansion of ( 1 x ) 1 ( 1 x 2 ) 1 ( 1 x 3 ) 1 (1-x)^{-1}(1-x^2)^{-1}(1-x^3)^{-1} about 0 0 .

What is your reasoning?

Arif Ahmed - 6 years, 5 months ago

How can we do that in terms other than 1-x to power -1

Chaitnya Shrivastava - 4 years, 8 months ago

Python solution:

n=0

for x in range(34):

     for y in range(51):

    for z in range(100):

        if x*3+y*2+z == 94:

            n += 1

print n \color{#EC7300}{\text{print n}}

784 \color{#3D99F6}{784}

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