Question

Four people A,B,C,D need to cross a rope
bridge to get back to their camp at night.
Unfortunately, they only have one
flashlight. The bridge is too dangerous to
cross without a flashlight, and it is only
strong enough to support two people at
any given time. A can cross the bridge in
1 minute, B in 2 minutes, C in 5 minutes,
and D takes 10 minutes to cross. What is
the minimum required time for A,B,C,D to
cross the rope bridge?

● 20 mins
● 17 mins
● 19 mins
● 21 mins​

Answer 1

Given :

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

The bridge is too dangerous to cross without a flashlight, and it is only strong enough to support two people at any given time.

Time taken by them to cross the bridge:

A = 1 min.

B = 2 min

C = 5 min.

D = 10 min.

Explanation:

A and B cross the bridge first (in 2 minutes)

A goes back with the flashlight in 1 min. (3 minutes)

C and D cross the bridge in 10 minutes (13 minutes)

B goes back with the flashlight takes time 2 min. (15 minutes)

Finally, A and B cross together again in 2 min. (17 minutes)

In 17 minutes they can cross the bridge.