Wikipedia:Reference desk/Archives/Mathematics/2008 September 26

= September 26 =

Correlation Coefficients
One number is missing from the data set below: fill it in to make the correlation coefficient equal to 0 (the answer is 1, I don't know how to get that tho)

x: 1,1,3,3   y: 2, 2, 3, (missing)

169.229.75.140 (talk) 20:04, 26 September 2008 (UTC)


 * Just say that the missing value is "a" and then calculate the correlation coefficient. You can then set it to 0 and solve for a. --Tango (talk) 21:06, 26 September 2008 (UTC)
 * Might be quicker to say zero correlation implies zero covariance and go from there. Zain Ebrahim (talk) 21:12, 26 September 2008 (UTC)

It's really simple by the routine algebraic method that "Tango" gave above, but you can also draw the scatterplot and ask what number would it have to be in order that the slope of the regression line be zero. That also makes it clear. Michael Hardy (talk) 22:14, 26 September 2008 (UTC)
 * With so few points, you're absolutely right - it's much easier that way. I gave a more general method, but it's really not necessary in this case because you can just use symmetries. --Tango (talk) 23:07, 26 September 2008 (UTC)

square feet
If someone wanted a deck 311 square feet how big is the deck in feet? —Preceding unsigned comment added by Jasonkrupel (talk • contribs) 21:01, 26 September 2008 (UTC) Jasonkrupel (talk) 21:04, 26 September 2008 (UTC).
 * That would depend on the shape. If you want a square deck, each side would need to be $$\sqrt{311}\,\mathrm{ft}$$, if you want any other rectangle, then any two numbers that multiply to make 311 would work. If you don't necessarily need it to be rectangular, then it could be any shape would could be scaled so that the area is 311 sq ft. --Tango (talk) 21:05, 26 September 2008 (UTC)


 * If rectangular then approximately:
 * 1 by 311 or,
 * 2 by 155 or,
 * 5 by 62 or,
 * 10 by 31 or,
 * 15 by 21 for examples.
 * If this is homework then the width times the length should equal 311 so, the length should be 311 divided by the width. hydnjo talk 00:37, 27 September 2008 (UTC)