The worked question on this page is original educational practice. It is not represented as a question from an official previous-year examination paper.
01 / UNDERSTANDING
Review the question
Write original paired-speed questions and require a substitution check. Then change only the distance to verify that recovered speeds remain the same while travel times scale.
02 / UNDERSTANDING
The concept in context
If both upstream and downstream speeds are known, their mean gives still-water speed and half their difference gives stream speed. These relations follow by adding and subtracting the two equations. They do not imply that real waterways have uniform conditions; the model’s constant speed and current assumptions belong in every practice explanation.
03 / UNDERSTANDING
A worked learning case
Original educational case. An original boat moves at 10 km/h in still water while the stream is 2 km/h. It travels downstream at 12 km/h and upstream at 8 km/h. A 24-km trip takes two hours downstream but three hours upstream. The same distance has different travel times because the stream changes speed relative to the riverbank.
ORIGINAL EDUCATIONAL PRACTICE
Try it before you check.
Original practice: Downstream speed is 15 km/h and upstream speed is 9 km/h. What is the stream speed under the stated model?
Show the answer and reasoning
3 km/h.
Subtract the upstream equation from the downstream equation: the still-water speed cancels, leaving twice the stream speed. The difference is 15 − 9 = 6 km/h, so the stream speed is 3 km/h. The still-water speed is 12 km/h, and substituting confirms 12 + 3 = 15 and 12 − 3 = 9.
Two traps to watch for.
- Using the full downstream-upstream difference as stream speed.
- Applying the downstream speed to an upstream travel time.
YOUR TOPIC-SPECIFIC LEARNING MAP
Learn from the attempt
Label boat speed and stream speed.
Write both ground-speed equations.
Substitute recovered values as a check.
Explain the idea, apply it to a new situation, then check what changed in your reasoning.
BANKERS TUTORIAL · SOURCE NOTES
Keep the source alongside your notes.
Official links provide subject context and authoritative reference material. This guide’s explanation, scenario and question are original Bankers Tutorial learning content.
- www.ibps.in https://www.ibps.in/
- www.ibps.in https://www.ibps.in/index.php/faq/
For IBPS & RRB preparation, check the current official notice before relying on changing dates, rules or examination requirements.
