Level
pending

A good puzzle....crack it...

Four friends A, B, C, D Need to cross the bridge.. They start on the same time to cross the bridge. A maximum of 2 peoples 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 ur brains...