Fatima walks 7 km south from the library, turns left and walks 4 km, then turns left again and walks 10 km. How far is she from the library now?

Explanation

1. 01

   Left from south is east; left from east is north.

2. 02

   North–south: 7 km south, then 10 km north, leaving 3 km north.

3. 03

   East–west: 4 km east.

4. 04

   Distance $= \sqrt{3^2 + 4^2} = 5$ km.