1. Sampling error calculation:

http://www.surveysystem.com/sscalc.htm

​

​

2. Standard normal distribution:

https://www.mathsisfun.com/data/standard-normal-distribution-table.html

​

​

3. T-value calculator:

https://goodcalculators.com/student-t-value-calculator/

​

​

4. F-value calculator:

https://www.danielsoper.com/statcalc/calculator.aspx?id=4