while this question is not homework, I found it to basic to be put in the "research" category.

I am comparing nutrient uptake rates of algae under different conditions and have taken samples with three replicates after different times (but also from different beakers each time, so I guess they are independent?). To get the rate for a specific timeframe I have to substract the previous mean from each mean, then divide the result to get to the uptake per hour.

In short: Substract, divide, and sometimes also multiply means with standard deviations from and with each other or single numbers.

I am doing all of this in excel and so far my resulting SDs are not right, since I just tried to puzzle together formulas with the limited knowldge I have. There seems to be no concise guide for this online. Unfortunately, I do not understand a page long essay with a dozen sum signs and other operators, so I hope someone here can help me.

Thank you for your time