Теория:

Study some exceptions for adjectives.
 
Запомните прилагательные, степени сравнения которых образуются не по правилу.

• Good – better – the best

• Bad – worse – the worst

• Little – less – the least

• Many/much – more – the most

• Old – elder – the eldest (когда говорим о членах семьи)

• Far – farther – the farthest

• Far – further – the furthest
  
  
Examples:

The train ticket is the least expensive.

Travelling by plane is the best variant.
 
Travel.jpg
  
Who is the eldest in your family?
Источники:
http://innonthedrive.com/traveling-by-car-plane-or-train