Wednesday, December 14, 2011

Puzzle 13 - Perfect cube

A ten digit number is a perfect cube.  It starts with two 7's and ends with one 7.  Find the number whose cube is this number.

4 comments:

SCHIZOPHRENIAC said...

7797729087 cube of 1983

SCHIZOPHRENIAC said...

solved through enumeration and reasoning.. any other better way to solve sir??

sravangottam said...

how to solve this kind of puzzle in simple manner

Vidyamanohar said...

Let the number be x.
Smallest 10 digit number is 1,000,000,000=1000^3
Further, smallest 10 digit number that starts with 8 (given number starts with 77)is 8,000,000,000=2000^3
So, x lies between 1000 and 2000 and close to 2000
As the last digit is 7, the number x ends with 3. 1993, 1983 are the two numbers need to be tried. 1983 is the required number.