Google Sheet formula for cumulative sum with condition

Question

I have a Google Sheet with the following layout:

  Number |  Counted?  |  Cumulative Total
    4    |     Y      |         4
    2    |            |         6
           


        

Answer 1

Try this in C2 and copy down:

= N(C1) + A2 * (B2 = "Y")

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Update

Doesn't seem to work with SUMIFS, but there is a very slow matrix multiplication alternative:

=ArrayFormula(MMult((Row(2:1000)>=Transpose(Row(2:1000)))*Transpose(A2:A1000*(B2:B1000="Y")), Row(2:1000)^0))