The Speed of a boat along the stream is 12 km/hr and against the stream is 8km/hr. The time taken by the boat to sail 24 km in still water is :

1. A

   2 hours

2. B

   2.4 hours

3. C

   3 hours

4. D

   1.2 hours

Appeared in: RRB Staff Nurse Delhi-2015

Explanation

• The speed of the boat in still water is the average of its speed along the stream (downstream) and against the stream (upstream).
• Calculation for speed in still water: (12 km/hr + 8 km/hr) / 2 = 10 km/hr.
• The time taken to travel a certain distance is calculated by the formula: Time = Distance / Speed.
• Calculation for time: 24 km / 10 km/hr = 2.4 hours.

Why Other Options Were Wrong

• Option A: A time of 2 hours would mean the boat's speed is 12 km/hr (24 km / 2 hr). This is the downstream speed, not the speed in still water.
• Option C: A time of 3 hours would mean the boat's speed is 8 km/hr (24 km / 3 hr). This is the upstream speed, not the speed in still water.
• Option D: A time of 1.2 hours would mean the boat's speed is 20 km/hr (24 km / 1.2 hr). This value (20) is the sum of the upstream and downstream speeds, not the boat's actual speed in still water.

Related Visual

• Visual 1: Diagram - An infographic illustrating the concepts of downstream motion (boat speed + stream speed) and upstream motion (boat speed - stream speed) to clarify the relationship between the different speeds.

Clinical Relevance

• Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Calculating time, speed, and distance for boats and streams as background academic context rather than a clinical decision trigger.
• This question tests quantitative aptitude, a common component of nursing and other competitive examinations.
• Developing accuracy and speed in mathematical calculations is a transferable skill, essential in clinical settings for tasks like calculating drug dosages, IV drip rates, and patient intake/output, where precision is critical for patient safety.
• What if the question asked for the time to travel 24 km downstream and then 24 km back upstream? The total time would be Time Downstream (24/12 = 2 hrs) + Time Upstream (24/8 = 3 hrs) = 5 hours.

How to Approach the Question

• First, identify the given information: Speed along the stream (downstream) = 12 km/hr, Speed against the stream (upstream) = 8 km/hr, and the distance to be covered in still water = 24 km.
• Recall the formula to calculate the speed of the boat in still water: Speed in still water = (Downstream Speed + Upstream Speed) / 2.
• Substitute the given values into the formula: (12 + 8) / 2 = 10 km/hr.
• Next, use the basic formula for time: Time = Distance / Speed.
• Calculate the time required to travel 24 km at the speed of 10 km/hr: 24 / 10 = 2.4 hours.
• Compare the result with the given options and select the correct one.

Concept Tested & Keywords

• Concept Tested: Calculating time, speed, and distance for boats and streams.
• Stem keywords: Speed of a boat, along the stream, against the stream, still water, time taken
• Lead-in keywords: The time taken

Question ID

QrAQ7lNEwTN31tqfY8zhrg

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