https://teamtreehouse.com/library/spreadsheet-basics/the-sumif-function
The SUMIF Function. SUMIF is a very handy function. It combines the SUM and IF functions to sum up values based on conditions you specify.
sumiffunctionspreadsheetbasicstreehouse
https://www.dummies.com/article/technology/software/microsoft-products/excel/adding-up-with-excel-2010s-sum-and-sumif-functions-191760/
addingexcelsumfunctions
https://www.extendoffice.com/documents/excel/5253-google-sheets-sumif-between-two-dates.html
Learn how to use formula in Google Sheets to sum values between two dates. Follow our step-by-step guide for accurate date-based conditional summing.
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