When a person increases his speed by 3 km/h, he reaches the office 10 minutes earlier. When he reduces his speed by 4 km/h, he reaches 20 minutes late, then what is his actual speed and what is the distance of his office from home?
-
12 km/hr , 126 km
-
21 km/hr , 64 km
-
18 km/hr , 21 km
-
25 km/hr , 125 km
C
Correct answer
Explanation
Let actual speed be v km/h and distance be d km. When speed increases to (v+3), time saved is 10 minutes: d/(v+3) = d/v - 10/60. When speed decreases to (v-4), time lost is 20 minutes: d/(v-4) = d/v + 20/60. Solving these equations yields v = 18 km/h and d = 21 km, which satisfies both conditions.