Maths help needed

chelsea -1.5 and blackburn +1.5 in English Premier League Soccer.
I figure Chelsea to average 2.0 goals.
I figure Blackburn to average 0.9 goals.
How do I compute the percentage chances of Chelsea covering and winning by 2 or more goals?
I have Stanford Wongs' book "sharp sports betting". I can work out the percentages if the margin is -0.5 or +0.5 using the 'poisson charts' in Stanfords book, but I can't figure it out for -1.5 or -2.5 etc.
Not even sure if this is an appropriate use of the Poisson charts!!!
Any help would be much appreciated.

[DougOzzzz]

Using the POISSON function in Excel I got a probability of 51.977% that Chelsea wins by 2+.

This was done by summing the probabilities of each possible result that Chelsea wins by 2.

4 columns. Column A goes from 0-20 (goals scored). Column B has the formula: =POISSON(A1,0.9,false). Column C has the formula =POISSON(A1,2.0,false). Column D has the formula, starting in cell A3, =C3*SUM(C$1:C1).
The sum of column D is the total probability.

[DougOzzzz]

I am a doofus. I responded to this post in both forums, not knowing I was switching back and forth.

To save myself from error the correct answer is 38.61% (had an error in my formula, though I explained it correctly.

Thanks. posted it in both forums not expecting such a quick response. BOTH responses of yours greatly appreciated. Have since worked out how to do formula on Excel (thanks to your other post)