已知Ymean = 55, Ysdv=9, SDE=4，求Correlation的值。
（原题：Your company currently has no way to predict how long visitors will spend on the Company’s web site. All it known is the average time spent is 55 seconds, with an approximately Gaussian distribution and standard deviation of 9 seconds. It would be possible, after investing some time and money in analytics tools, to gather and analyzing information about visitors and build a linear predictive model with a standard deviation of model error of 4 seconds.）
求各位大神帮忙><。。。最好能附上步骤，谢谢！！