Product of a Triple

How many ordered triples of positive integers ( a , b , c ) (a, b, c) are there such that a b c = 6 4 abc = 6^ 4 ?


The answer is 225.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

1 solution

Christopher Boo
Mar 16, 2014

a b c = 6 4 abc=6^4

a b c = 2 4 × 3 4 abc=2^4\times3^4

Let a = 2 a 1 × 3 a 2 a=2^{a_1}\times3^{a_2} , b = 2 b 1 × 3 b 2 b=2^{b_1}\times3^{b_2} , c = 2 c 1 × 3 c 2 c=2^{c_1}\times3^{c_2}

Then the equation becomes

( 2 a 1 × 3 a 2 ) ( 2 b 1 × 3 b 2 ) ( 2 c 1 × 3 c 2 ) = 2 4 × 3 4 (2^{a_1}\times3^{a_2})(2^{b_1}\times3^{b_2})(2^{c_1}\times3^{c_2})=2^4\times3^4

2 a 1 + b 1 + c 1 × 3 a 2 + b 2 + c 2 = 2 4 × 3 4 2^{a_1+b_1+c_1}\times3^{a_2+b_2+c_2}=2^4\times3^4

Then we have

  1. a 1 + b 1 + c 1 = 4 a_1+b_1+c_1=4

  2. a 2 + b 2 + c 2 = 4 a_2+b_2+c_2=4

By the technique Stars and Bars ,

The combinations of ( a 1 , b 1 , c 1 ) = ( a 2 , b 2 , c 2 ) = ( 6 2 ) = 15 (a_1,b_1,c_1)=(a_2,b_2,c_2)={6\choose2}=15

Then, we multiply the arrangements of them to find the total combinations of a 1 , a 2 , b 1 , b 2 , c 1 , c 2 a_1,a_2,b_1,b_2,c_1,c_2 , which is

1 5 2 = 225 15^2=225

I found this solution helpful, thanks.

Silas Hundt Staff - 7 years, 2 months ago

Log in to reply

Thanks, and I fixed some typing errors...

Christopher Boo - 7 years, 2 months ago

Superb.

Soham Dibyachintan - 7 years, 2 months ago

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...