I am trying to get a previously built worksheet to properly run some
formulas. We have three product types, designated "C", "P", and "M". The
worksheet has a column with one of these designations entered in each cell,
with the weight associated with each entry in an adjoining cell in the next
column. The formula calls for the worksheet to sum the weights by product
type, using a nested SUM(IF) command
=SUM(IF($D$2:$D$400="C",$E$2:$E$400)), and likewise for the other two types.

The problem is that this formula works great when surrounded by brackets {
}, but not otherwise. Attempts to manually enter or otherwise force the
brackets prove fruitless, as including the = sign hides the indication that
this is a formula. Re-entering the formula in a clean cell also does no good.

What am I doing wrong, and how do I fix it? Many thanks.
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