Maths question from Social Forest Worker exam, 2026 by JKSSB
A train covers a distance S at a speed U. If its speed is increased by 10km / h the travel time reduces by 2 hours, and if increased by 20km / h the time reduces by 3 hours. Find the distance S.
Last updated Jul 21, 2026
Correct Answer:
Option C —
120 km
1. Set up the Relationships
Let the original speed be U kilometers per hour and the original time be T hours.
The total distance S is calculated as speed multiplied by time.
For the first scenario, increasing the speed by 10 kilometers per hour decreases the travel time by 2 hours. Multiplying this new speed by the new time gives the distance S, which simplifies to: 10 times T minus 2 times U equals 20.
For the second scenario, increasing the speed by 20 kilometers per hour decreases the travel time by 3 hours. Multiplying this new speed by the new time gives the distance S, which simplifies to: 20 times T minus 3 times U equals 60.
2. Solve for Time and Speed
From the first scenario, expressing U in terms of T gives: U equals 5 times T minus 10.
Substituting this expression for U into the second scenario equation gives: 20 times T minus 3 times the quantity 5 times T minus 10 equals 60.
Expanding and combining like terms yields: 5 times T plus 30 equals 60, which means 5 times T equals 30.
Dividing 30 by 5 reveals the original time T is 6 hours.
Plugging 6 back into the speed formula gives U equals 5 times 6 minus 10, which means the original speed U is 20 kilometers per hour.
3. Calculate Distance S
The total distance S is the original speed multiplied by the original time.
Multiplying 20 kilometers per hour by 6 hours yields a total distance of 120 kilometers.
Conclusion
Correct Answer: C) 120 km
Answer verified by Quintessence Classes faculty — Karan Nagar, Srinagar.
