Integers here! Max?

Let x , y , z x,y,z be three non-negative integers such that x + y + z = 10 x+y+z=10 . The maximum possible value of x y z + x y + y z + z x xyz+xy+yz+zx is:

64 73 52 69

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.

2 solutions

Mohit Kuri
Oct 29, 2014

For max. Value all must be around same values ( what I apply to All problems) thus I tried 3,3,4 and there is was. :)

Cool! Its a KVPY 2013 problem! And I did it the same way there!

Pranjal Jain - 6 years, 7 months ago

Log in to reply

I tried it first time pranal here only . But going to solve KVPY paper 2013 tomorrow as KVPY is on 2 November.

Mohit Kuri - 6 years, 7 months ago
Jared Low
Nov 30, 2014

Note that the first condition is equivalent to ( x + 1 ) + ( y + 1 ) + ( z + 1 ) = 13 (x+1)+(y+1)+(z+1)=13

To answer the question would be the same as finding the maximum possible value of

x y z + x y + y z + z x + x + y + z + 1 xyz+xy+yz+zx+x+y+z+1

= x y z + x y + y x + z x + 11 =xyz+xy+yx+zx+11

= ( x + 1 ) ( y + 1 ) ( z + 1 ) =(x+1)(y+1)(z+1) , with ( x + 1 ) , ( y + 1 ) , ( z + 1 ) (x+1),(y+1),(z+1) all being positive integers.

Now assume w.l.o.g. that x y z x\leq y\leq z or equivalently x + 1 y + 1 z + 1 x+1 \leq y+1 \leq z+1 .

Checking for the cases x + 1 = 1 , 2 , , 4 x+1=1,2, \dots, 4 (since if x 4 x \geq 4 , we have x + y + z 12 x+y+z \geq 12 , a contradiction), we have the case x = 3 , y = 3 , z = 4 x=3, y=3, z=4 giving a maximum possible value for x y z + x y + y z + z x xyz+xy+yz+zx as ( 3 + 1 ) ( 3 + 1 ) ( 4 + 1 ) 11 = 69 (3+1)(3+1)(4+1)-11=\boxed{69}

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...