Qualcomm Interview Questions: Bridge and torch problem : Four people come to a river in th

Bridge and torch problem : Four people come to a river in the night. There is a narrow bridge, but it can only hold two people at a time. They have one torch and, because it's night, the torch has to be used when crossing the bridge. Person A can cross the bridge in 1 minute, B in 2 minutes, C in 7 minutes, and D in 10 minutes. When two people cross the bridge together, they must move at the slower person's pace. What is the least time taken for them to get across the bridge?

VINOTH BABU

17 min

RAHUL TIWARI

13d

1. A and B cross the bridge together (2 minutes). Torch is with them. 2. A returns with the torch (1 minute). Total time: 3 minutes. 3. C and D cross the bridge together (10 minutes). Torch is with th...read more

Mihir Vikram Singh Chauhan

22d

10 min A uses torch and crosses with B That is 2 minutes. Then A returns and crosses with C that is 7 minutes. => 2+1+7=10

Satya Narayana Reddy

27d

17 minutes

Parvez Hakim

29d

Step 1: A and B cross the bridge. A comes back. Time taken 3 minutes. Now B is on the other side. Step 2: C and D cross the bridge. B comes back. Time taken 8 + 2 = 10 minutes. Now C and D are on the ...read more

Anonymous

1mo

Sir, this question is wrong as long as it does not measure the length of the pool or the speed of the bucket.

Anonymous

1mo

Anonymous

1mo

Adithya CP

1mo

Total time taken will be 21 minutes

Anonymous

1mo

kiran babu

2mo

17 minutes

Sunita Tiwary

2mo

They will cross bridge in total 10 minutes. D will start with torch every time in his hand. First A will join him and reach other side of the bridge , followed by B who will reach the other side in 2 ...read more

Anonymous

2mo

A @ D will take to 10 minutes to cross the bridge so all of them will take 21 minutes to cross the bridge

Devika K.S

2mo

ex -

State Bank of India

The bridge and torch problem (also known as The Midnight Train[1] and Dangerous crossing[2]) is a logic puzzle that deals with four people, a bridge and a torch. It is in the category of river crossin...read more

Hillan Shaba

2mo

currently not working

A&D will take 10 minutes to cross the bridge. So all of them will take 21 minutes to cross the bridge.

Praveen Singh

2mo

7 minutes with each for crossing the bridge.

Akshay Lilhare

2mo

Step 1: 2 minutes (A and B cross) Step 2: 1 minute (A returns) Step 3: 10 minutes (C and D cross) Step 4: 2 minutes (B returns) Step 5: 2 minutes (A and B cross again) Total Time = 2 + 1 + 10 + 2 + 2 ...read more

Anonymous

2mo

17 minutes

Hillan Shaba

2mo

currently not working

17 minutes

Ankit Pachauri

2mo

17 minutes with each for crossing the bridge

krishnakddinker9555

2mo

works at

Buyume

How it solved

Anonymous

3mo

17 minutes

Piyush Bhatt

3mo

17 minutes

Anonymous

3mo

17 minutes

Venkatesh Karthik

3mo

The least time taken for all four people to get across the bridge is 17 minutes

opulentcornetto

3mo

currently not working

They are all cross the bridge 15 minutes everyone

Anonymous

3mo

A+B = 2 A returns = 1 C+D = 10 B returns = 2 A+B = 2 Total = 17 mins

naveen kumari

3mo

Ekansh Agnihotri

3mo

-- A + B = 2min -- A back = 1min -- C + D = 10min -- B back = 2min -- A + B = 2min -- Therefore 17 min

Anonymous

3mo

A and B cross in 2 minutes and C and D in 10 minutes.. This,least time taken=12 minutes..

Anonymous

3mo

12 minutes

Anonymous

3mo

21mins

Lavneesh Yadav

4mo

21 mins

Srinivas Krishnan

4mo

21 mins

Sandra shirisha

3mo

24mins

Anonymous

4mo

Kavya Narkuti

4mo

7 minutes

Vivacious Priya

4mo

A and B cross in 2 minutes= 2 min A returns in 1 minutes= total 3 min C and D cross in 8 minutes =total 8+3=11 minutes B returns in 2 minutes= 11 +2 =13 minutes A and B cross in 2 minutes =total 13+2=...read more

Anonymous

3mo

how can C and D cross in 8 mins? doesnt make sense. answer will be 21 mins.

Virendra Saini

4mo

Four people come to a river in the night. There is a narrow bridge, and it can only hold two people at a time. They have one torch and, because it's night, the torch has to be used when crossing the b...read more

Anonymous

4mo

Answer is "No"

Anonymous

4mo

MANVEL M

4mo

Total Time: 2 + 1 + 10 + 2 + 2 = 17 minutes Therefore, the least time taken for all four people to get across the bridge is 17 minutes.

Anonymous

4mo

21 minute

Sandip Salunkhe

4mo

A and B cross: 2 minutes A returns: 1 minute C and D cross: 10 minutes B returns: 2 minutes A and B cross: 2 minutes Total time: 2+1+10+2+2=17 minutes

Anonymous

5mo

17 Minutes

Anonymous

4mo

9.2

Anonymous

5mo

17minutes

Chheetar Lal Sen

5mo

works at

Larsen & Toubro Limited

17 Minutes

Anonymous

5mo

Arnab Sen

5mo

A, B goes -> 2 mins A come back -> 1 min C, D goes -> 10 mins B comes back -> 2 mins A, B goes -> 2 mins Total 17 mins

SHAJEETH S

5mo

student at

Sri Krishna College of Engineering and Technology, Coimbatore

1st A & B pair and cross at 2 mins. 2nd C & D pair and can cross at 10 mins. so total 12 mins they can cross the bridge at least time.

Arnab Sen

5mo

what about the torch when C,D goes?. someone has to come back with the torch

Deepshikha Mehta

5mo

17 minutes

Aayush

5mo

In 17 minutes

Anonymous

5mo

17 minutes

Mohammed Salal

5mo

17 A+B-2 A-1 C+D-10 B-2 A+B-2 =2+1+10+2+2

vikram shekhawat

5mo

1st to and fro- A+B=3 2nd to and fro- A+C=8 3rd one side-A+D=10 Total=21 Minutes

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