Q. Two persons A and B working together, can dig a trench in 8 hours, while A alone can dig it in 12 hours. In how many hours B alone can dig the same trench?
a) 24 hours
b) 30 hours
c) 26 hours
d) 28 hours
Correct Answer: a) 24 hours
Question from UPPSC Prelims CSAT 2025
Explanation:
Let the total work be 1 trench. A’s rate = 1/12 trench/hour. Together (A+B) rate = 1/8 trench/hour.
Therefore, B’s rate = 1/8 − 1/12 = (3−2)/24 = 1/24 trench/hour.
Time taken by B alone = 1 ÷ (1/24) = 24 hours.
