Question

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: 8 minutes to cross bridge
D: 11 minutes to cross bridge

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

Answer 1

A total of 23 minutes will be required for them to cross the bridge.

Step-by-step Explanation:

• A will take everyone one by one with the lamp as he is the fastest in them and can come back early with a lamp to save time.

• When A will cross the bridge with B it will take them 2 minutes to go and 1 minute for A to come back, that makes 3 minutes total.

• Then he will take C and comes back it will take them 9 minutes in total.

• In the end, he will go with D and it will take them 11 minutes.

Answer 2

Answer:

23 min

Step-by-step explanation:

A, being the fastest among them will working for showing path, all the time.

At first,

   A___   time = 2 min( time by B)

   B __/

Now, A comes back , taking 1 minute. Total till now = 2 + 1 = 3 min

 A___   time = 8  min(time by C)

 C__/

Now, again A come back, taking 1 min, total = 3 + 8 + 1 = 12 min

 A___    time = 11 min(time by D)

 D__/

As, now, there is none left. A won't return. So total time = 12 + 11 = 23 min