Google Data Scientist interview questions

You have a google app and you make a change. How do you test if a metric has increased or not?

1. Why use feature selection? If two predictors are highly correlated, what is the effect on the coefficients in the logistic regression? What are the confidence intervals of the coefficients? 2. K- mean and Gaussian mixture model: what is the difference between K-mean and EM? 3.How to decided k? 4.When using Gaussian mixture model, how do you know it is applicable? (Normal distribution) 4.If the labels are known in the clustering project, how to evaluate the performance of the model? In my project, I use adjusted rank index? But I forgot how it is defined.