Could someone explain to me why these two differ in value. Is it because of rounding and that it's a decimal number?
$(1.000218475^{23}- 1)*42731.41 + (1.000218475^{9}- 1)*42731.41 $ = 299.33
$(1.000218475^{32}- 1)*42731.41 $ = 299.75
Not sure what to tag, sorry.
You seem to expect that $a^b + a^c$ equals $a^{b+c}$. In general, it does not.
For example, $1^2 + 1^3 = 1+1=2$, but $1^{2+3}=1^5=1$.