Add Cells From a Different Sheet

I teach a coding course where some of my lessons have combined classes come to me. We recently had some new students and I wanted to see what the updated number of students in the class would be. 

I started by simply adding the numbers. I found that you can hold CMD and click on all the cells and Google Sheets will automatically give you the sum of the numbers.

But what happens when students enter or leave the school? I have to manually update my sheets. 

Fortunately, I have access to the main spreadsheet with the class numbers. 

Since I want an up-to-date sheet, I knew I could use the IMPORTRANGE function to get the information. Then I needed to add them together using the SUM function. 

The final formula looked like this below.

=SUM(IMPORTRANGE("sheetURL", "Sheet!C28:C29")+IMPORTRANGE("sheetURL", "Sheet!C30:C31"))