Building on Bob's proposal:

Enter with Ctrl+Shift+Enter

=SUM(POISSON($I$1:$I$8,PS1,0)*POISSON($J$1:$J$8,PS 2,0)

PS1: is named range =0.5*(C1+Sheet1!C52)
PS2: is named range =0.5*(C1-Sheet1!C52)

I1:I8 contain values for PS1
J1:J8 contain values for PS2

HTH


"Toppers" wrote:

Enter as an array formula with Ctrl+Shift+Enter

=SUM(POISSON({1,2,2,3,4,5,7,2},0.5*B1,FALSE)*POISS ON({0,0,0,0,0,6,0,0},0.5*B2,FALSE))


b1= =C1+Sheet1!C52
b2= =C1-Sheet1!C52

with C12=4, C52=2 I returned a result of 0.4991536 using your posing and the
solution above.

HTH

"phil2006" wrote:


I have the following formula:
(POISSON(1,0.5*(C1+Sheet1!C52),FALSE))*(POISSON(0, 0.5*(C1-Sheet1!C52),FALSE))+(POISSON(2,0.5*(C1+Sheet1!C52) ,FALSE))*(POISSON(0,0.5*(C1-Sheet1!C52),FALSE))+(POISSON(2,0.5*(C1+Sheet1!C52) ,FALSE))*(POISSON(0,0.5*(C1-Sheet1!C52),FALSE))+(POISSON(3,0.5*(C1+Sheet1!C52) ,FALSE))*(POISSON(0,0.5*(C1-Sheet1!C52),FALSE))+(POISSON(4,0.5*(C1+Sheet1!C52) ,FALSE))*(POISSON(0,0.5*(C1-Sheet1!C52),FALSE))+(POISSON(5,0.5*(C1+Sheet1!C52) ,FALSE))*(POISSON(6,0.5*(C1-Sheet1!C52),FALSE))+(POISSON(7,0.5*(C1+Sheet1!C52) ,FALSE))*(POISSON(0,0.5*(C1-Sheet1!C52),FALSE))+(POISSON(2,0.5*(C1+Sheet1!C52) ,FALSE))*(POISSON(1,0.5*(C1-Sheet1!C52),FALSE))


and need to add more, is there anyway I can reduce the size because i
am being told it is too long!

Thanks


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