No woods or log's required!

Algebra Level 3

If 2 7 x = 6 4 y = 12 5 z = 60 27^{x} = 64^{y} = 125^{z} = 60 , find the value of 2013 x y z x y + y z + x z \large\frac{2013xyz}{xy+yz+xz} .


The answer is 671.

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.

4 solutions

Since we get 3 equations, we can say that 2 7 x = 60 , 6 4 y = 60 , 12 5 z = 60 27^{x} = 60, 64^{y} = 60, 125^{z} = 60 .

Take a x,y,z-th root we get...

27 = 6 0 1 x , 64 = 6 0 1 y , 125 = 6 0 1 z 27 = 60^{\frac{1}{x}}, 64 = 60^{\frac{1}{y}}, 125 = 60^{\frac{1}{z}} .

We multiply 3 equations we get...

27 × 64 × 125 = 6 0 1 x + 1 y + 1 z 27\times64\times125\ = 60^{\frac{1}{x}+\frac{1}{y}+\frac{1}{z}}

6 0 3 = 6 0 1 x + 1 y + 1 z 60^{3} = 60^{\frac{1}{x}+\frac{1}{y}+\frac{1}{z}}

1 x + 1 y + 1 z = 3 \frac{1}{x}+\frac{1}{y}+\frac{1}{z} = 3 ....

Simplify that we get x y + y z + z x x y z = 3 \frac{xy+yz+zx}{xyz} = 3

x y z x y + y z + z x = 1 3 \frac{xyz}{xy+yz+zx} = \frac{1}{3}

Therefore: 2013 x y z x y + y z + z x = 2013 3 = 671 \frac{2013xyz}{xy+yz+zx} = \frac{2013}{3}\ = \boxed{671} ~~~

Note that we can take the x,y,z-th root because x,y,z are positive numbers. (not necessary greater than 1.)

Samuraiwarm Tsunayoshi - 7 years, 5 months ago

Wonderful and elegant !!

anoir trabelsi - 7 years ago

yes, I too did it the same way

Raushan Sharma - 6 years, 3 months ago

Log in to reply

Exactly the same

Rama Devi - 6 years ago

did the exact same way.... the best solution, indeed

Kartik Sharma - 6 years, 12 months ago
Shravan Jain
Mar 3, 2014

27 x = 64 y = 125 z = 60 x = log 27 60 , y = log 64 60 , z = log 125 60 N o w , 2013 x y z x y + y z + z x = 2013 1 x + 1 y + 1 z ( D i v i d i n g n u m e r a t o r a n d d e n o m i n a t o r b y x y z ) 2013 x y z x y + y z + z x = 2013 1 log 27 60 + 1 log 64 60 + 1 log 125 60 = 2013 log 60 27 + log 60 64 + log 60 125 = 2013 3 log 60 ( 3 × 4 × 5 ) = 2013 3 log 60 ( 60 ) = 2013 3 = 671 { 27 }^{ x }={ 64 }^{ y }={ 125 }^{ z }=60\\ \therefore \quad x=\log _{ 27 }{ 60 } ,\quad y=\log _{ 64 }{ 60 } ,\quad z=\log _{ 125 }{ 60 } \\ Now,\frac { 2013xyz }{ xy+yz+zx } =\quad \frac { 2013 }{ \frac { 1 }{ x } +\frac { 1 }{ y } +\frac { 1 }{ z } } \quad (Dividing\quad numerator\quad and\quad denominator\quad by\quad xyz)\\ \therefore \frac { 2013xyz }{ xy+yz+zx } =\quad \frac { 2013 }{ \frac { 1 }{ \log _{ 27 }{ 60 } } +\frac { 1 }{ \log _{ 64 }{ 60 } } +\frac { 1 }{ \log _{ 125 }{ 60 } } } \\ \qquad \qquad \qquad \quad =\quad \frac { 2013 }{ \log _{ 60 }{ 27 } +\log _{ 60 }{ 64 } +\log _{ 60 }{ 125 } } \\ \qquad \qquad \qquad \quad =\quad \frac { 2013 }{ 3\log _{ 60 }{ (3\times 4\times 5) } } =\frac { 2013 }{ 3\log _{ 60 }{ (60) } } =\frac { 2013 }{ 3 } =\boxed { 671 }

Did the same!!!

Tanya Gupta - 7 years, 3 months ago

I also did the same solution.

Rhoy Omega - 7 years, 2 months ago

Did the same

Akhilesh Prasad - 7 years, 1 month ago
Christopher Boo
Mar 1, 2014

Firstly, we have no direction on how to solve this problem, we can either handle

2 7 x = 6 4 y = 12 5 z = 60 27^x=64^y=125^z=60

or

2013 x y z x y + y z + x z \dfrac{2013xyz}{xy+yz+xz}

We cannot really see the connection between these two expressions and the first equation seems complicated if we touch it. So, what I did is simplify the second expression:

2013 x y z x y + y z + x z \dfrac{2013xyz}{xy+yz+xz}

= 2013 ( 1 x y + y z + x z x y z ) =2013\Big(\dfrac{1}{\frac{xy+yz+xz}{xyz}}\Big)

= 2013 ( 1 1 x + 1 y + 1 z ) =2013\Big(\dfrac{1}{\frac{1}{x}+\frac{1}{y}+\frac{1}{z}}\Big)

Now, the expression become more simpler, the connection between them is as below

  1. 6 0 1 x = 27 60^\frac{1}{x}=27

  2. 6 0 1 y = 64 60^\frac{1}{y}=64

  3. 6 0 1 z = 125 60^\frac{1}{z}=125

Then, we do as below:

6 0 1 x + 1 y + 1 z = 3 3 × 4 3 × 5 3 = 6 0 3 60^{\frac{1}{x}+\frac{1}{y}+\frac{1}{z}}=3^3\times4^3\times5^3=60^3

So,

1 x + 1 y + 1 z = 3 {\dfrac{1}{x}+\dfrac{1}{y}+\dfrac{1}{z}}=3

Substitute this to the given expression we have:

= 2013 ( 1 1 x + 1 y + 1 z ) =2013\bigg(\dfrac{1}{\frac{1}{x}+\frac{1}{y}+\frac{1}{z}}\bigg)

= 2013 ( 1 3 ) =2013(\frac{1}{3})

= 671 =671

Akash Deep
May 21, 2014

2 7 x = 3 3 x = 6 4 y = 2 6 y = 12 5 z 27^{x} = 3^{3x} = 64^{y} = 2^{6y} = 125 ^{ z} = 5 3 z = 60 5 ^ {3z} = 60 and on multiplying 3 equations we get [ 3 x ( 2 2 ) y 5 z ] 3 = 6 0 3 [ 3 ^ {x} * (2 ^ {2}) ^ {y} * 5 ^ {z}] ^ {3} = 60 ^ {3} and further we get 3 x 2 2 y 5 z = 3 1 2 2 5 1 3 ^{ x }* 2 ^ {2}y * 5 ^ {z} = 3 ^ {1} * 2 ^ {2} * 5 ^ {1} and hence we get x = y = z = 1 and then 2013 x y z ( x y + y z + x z ) \frac{2013 * x * y * z} {(xy + yz + xz)} = 2013 3 = 671 \frac{2013}{3 }= \boxed{671}

If x = y = z = 1, then we have 27 = 64 = 125 = 60.

Dwight House - 3 years, 9 months ago

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...