Hi,

I got different results for the correlation-coefficient r

x y

----

1 3

2 3

3 3

4 3

Excel returns div/0

TI 84+ returns blank

other programs returns 0.0

my opinion is div/0, because the standard deviation is 0

BUT my maths book has a multiple choice answer : a)-1 b)0 c)1

no div/0 answer possible.

Thanks for reading