Do anyone know how toexplain the Pearson's R correlation problems, meaning how did the square root of R2=0.785. The begining...

Do anyone know how toexplain the Pearson's R correlation problems, meaning how did the square root of R2=0.785. The begining of the problem ws, the hours that students studied and the grade they recieved.

Y=1.5608x + 55.767. This was calculated from a scatterplot example.