Group employees by salary range (Low/High) .GroupBy(e => e.Salary > 75000? "High" : "Low")

Short answer: var salaryGroups = employees .Select(g => new { Range = g.Key, Count = g.Count() });

Example code

var salaryGroups = employees
.Select(g => new { Range = g.Key, Count = g.Count() });

Real-world example (ShopNest)

A sales report joins orders and customers, then GroupBy(c => c.City) to show revenue per city.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.