Variance explained by a regression

In a simple linear regression of YY on XX you measure Cov⁡(X,Y)=3\operatorname{Cov}(X,Y)=3, Var⁡(X)=4\operatorname{Var}(X)=4, and Var⁡(Y)=9\operatorname{Var}(Y)=9. What fraction of the variance of YY does the fitted line explain (the R2R^2)? (to 2 decimals)

Show hints (2)+
  1. R^2 equals the squared correlation, rho^2 = Cov(X,Y)^2 / (Var(X) Var(Y)).
  2. Do not stop at the slope Cov/Var(X); square the correlation.

Answer

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0.25 (± 0.01)

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