When a boat moves at an average speed of 25 kmph it reaches its destination on time. When its average speed becomes 35 kmph, then it reaches its destination 15 minutes early. Find the length of journey rounded to two decimal places. Choose the correct choice from the following answers:
A) 18.67 km
B) 24.50 km
C) 21.88 km
D) 17.98 km
E) None
Sol.   Difference between timings = 15 min = 1/4 hr.   Let the length of journey be x km.   Then, x/25 - x/35 = 1/4   â‡” 7x - 5x = 43.75   â‡” 2x = 43.75   â‡” x = 21.88 km.   Answer 21.88 km
<result>C</result>
When a boat moves at an average speed of 25 kmph it reaches its destination on time. When its average speed becomes 35 kmph, then it reaches its destination 15 minutes early. Find the length of journey rounded to two decimal places.