Cross the bridge – Puzzle

Crack this puzzle…

Four friends A, B, C, D need to cross a bridge..

A maximum of 2 people can cross at a time..

It is night and they have just 1 lamp.

People that cross the bridge must carry the lamp to see the way..

A pair must walk together at the speed of slower person…

Speeds of

A: 1 minute to cross bridge

B: 2 minutes to cross bridge

C: 7 minutes to cross bridge

D: 10 minutes to cross bridge

Now question is… “what is the total minimum time required by all 4 friends to cross the bridge….?

Scratch your brains… ?

Take your own time.

Ans: A & B = 2, B Returns    = 2, C & D =10, A returns    = 1, A & B = 2

Total = 17