All about flooble | fun stuff | Get a free chatterbox | Free JavaScript | Avatars    
perplexus dot info

Home > Just Math
Mental Cube Root (Posted on 2004-03-10) Difficulty: 2 of 5
If the cube root of 1331 is 11 and the cube root of 1728 is 12, what is the cube root of 1442897?

(Do this one in your head - no writing or calculators allowed!)

See The Solution Submitted by Gamer    
Rating: 2.6667 (9 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
Solution Solution to the Problem Comment 6 of 6 |
The number is greater than 1.331*10^6 but less than 1.728*10^6 and so; the cube root must lie between 111 and 119 inclusively.....(i)

Since the given positive integer is  congruent to 7 when reduced in modulo 10, it follows that the required cube root  must possess the form 3 ( Mod 10).

Consequently, from (i) it now follows that  the required cube root must be 113. 

Edited on September 12, 2007, 11:28 am
  Posted by K Sengupta on 2007-03-09 05:13:08

Please log in:
Login:
Password:
Remember me:
Sign up! | Forgot password


Search:
Search body:
Forums (0)
Newest Problems
Random Problem
FAQ | About This Site
Site Statistics
New Comments (4)
Unsolved Problems
Top Rated Problems
This month's top
Most Commented On

Chatterbox:
Copyright © 2002 - 2017 by Animus Pactum Consulting. All rights reserved. Privacy Information