Answer:
The shortest time needed for all four of them to cross the bridge = 17 minutes
Explanation:
As given , to cross the bridge
Person 1 takes 1 minute,
Person 2 takes 2 minutes,
Person 3 takes 5 minutes, and
Person 4 takes 10 minutes.
For the first time ,
Person 1 and Person 2 will go to cross the bridge
As Person 2 takes 2 minutes
So, total time taken by Person 1 and person 2 together will be 2 minutes
Now,
Person 1 will come back with flashlight.
He takes 1 minutes.
So, Total time becomes 2 + 1 = 3 minutes
Then,
Person 3 and Person 4 will cross the bridge
As Person 4 takes 10 minutes
So, total time taken by Person 3 and person 4 together will be 10 minutes
So, Total time becomes 3 + 10 = 13 minutes
Now,
Person 2 will come back with flashlight.
He takes 2 minutes.
So, Total time becomes 13 + 2 = 15 minutes
Then,
Person 1 and Person 2 will cross the bridge
As Person 2 takes 2 minutes
So, total time taken by Person 1 and person 2 together will be 2 minutes
So, Total time becomes 15 + 2 = 17 minutes
∴ we get
The shortest time needed for all four of them to cross the bridge = 17 minutes
