One of my favorite challenges to give data science candidates is to generate a dataset with a column for date and a column for attendance. With some added noise

One of my favorite challenges to give data science candidates is to generate a dataset with a column for date and a column for attendance. With some added noise, attendance started at 1000 and decreased by two per day. I showed a year of data and asked them to predict the value a month from now. It was astonishing how many candidates come up with complicated approaches, like randomizing the data into train/test/validation groups (the wrong thing to do for a time series). I don't think any of my applicants so far has double clicked the file to open it in Excel, plotted the data, and saw just how linear it was. You could follow the line with your finger and come up with a decent prediction. Maybe do that in ggplot2 or matplotlib if you want to show you can write code. Even a quick lm(dta$attendance ~ dta$date) would get you great results.