Sunday, June 26, 2011

cube root of 1729.03

..need to find the cube root of 1729.03

"The number was 1729.03. I happened to know that a cubic foot contains 1728 cubic inches, so the answer is a tiny bit more than 12. The excess, 1.03, is only one part in nearly 2000, and I had learned in calculus that for small fractions, the cube root's excess is one-third of the number's excess. So all I had to do is find the fraction 1/1728, and multiply by 4 (divide by 3 and multiply by 12). So I was able to pull out a whole lot of digits that way."

Saturday, June 25, 2011

square of the numbers nearer to 50

To find the square of the numbers nearer to 50:
subtract the 100 times of the difference of the number and 50, from 2500 and then add square of the difference. Example
49^2=2500-100+1=2401
48^2=2500-200+4=2304