Maths help for Novice

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.
I'm not even sure if this is an appropriate use of the Poisson charts.
Any help would be much appreciated.

[DougOzzzz]

Using Excel, I got a probability of 51.977% for Chelsea to win by 2+.

This was done by using the POISSON function in Excel, and summing the products of each possible result where Chelsea wins by 2+ goals.

Thanks for the reply. Will have to do some study to see if I can work it out for myself next time.
Thanks again.

[DougOzzzz]

I thought I posted this before but it didn't show up... anyway, here is what the Excel spreadsheet looks like:

4 columns -

Column A has goals scored, from 0-20.
Column B has the formula =POISSON(A1,0.9,false) The A1 will change based on the current row.
Column C has the formula =POISSON(A1,2.0,false)
Column D has the formula, starting in cell D3, =C3*SUM(A$1:A1). The first 1 following the dollar sign remains constant, while the 2nd 1 will always be the current row minus 2. The sum of column D is the total probability.

[DougOzzzz]

I had an error in one of my formulas. Actual total should be 38.613%