Data Science interview questions for freshers

A normal distribution is a symmetric bell curve fully described by mean and standard deviation.

In a continuous uniform distribution every value in an interval is equally likely.

Skewness describes asymmetry: right skew has a long high tail, left skew a long low tail.

A bimodal distribution has two peaks, often because two subgroups are mixed, such as weekday and weekend usage.

A time series is a sequence of observations ordered in time, such as daily active users or hourly revenue.

A trend is a long-run increase or decrease in the level of the series.

Seasonality is a repeating pattern at a fixed period, such as weekly cycles or holiday spikes.

A KPI is a key performance indicator: a metric the business uses to judge success at a chosen grain and window.

Conversion rate is conversions divided by eligible opportunities in a period, such as purchases over unique visitors.

Churn rate is the share of customers who stop using or paying during a period, among those who could have churned.

Mean is the average.

It measures spread around the mean.

It keeps all left rows and matching right rows, with nulls when no match.

Duplicates inflate counts and leak between train and test if not handled.

Shape, dtypes, missingness, obvious outliers, and a few value counts.

They run faster than Python row loops on large frames.