36. A train runs from Howrah to Bandel at an average speed of 20km/hr and returns at an average speed of 30 km/hr. The average speed (in km/hr) of the train in the whole journey is.
(A) 20 km/hr
(B) 22.5 km/hr
(C) 24 km/hr
(D) 25 km/hr
Answer:
(C) 24 km/hr
Explanation:
When the distance is constant, the formula for average speed is 2xy/(x+y). Substituting the values: (2×20×30)/(20+30)=1200/50=24 km/hr.
37. A man travelled a certain distance by train at the rate of 25 km/hr and walked back at the rate of 4 km/hr. If the whole journey took 5 hours 48 minutes, the distance was.
(A) 25 km
(B) 30 km
(C) 20 km
(D) 15 km
Answer:
(C) 20 km
Explanation:
Total time = 5 hrs 48 mins=29/5 hours. Let the distance be D. The equation is D/25+D/4=29/5. Solving gives (4D+25D)/100=29/5 29D/100=29/5 D=100/5=20 km
38. A can do a certain work in 10 days and B can complete same work in 15 days if they work together then in how many days works gets done?
(A) 6 days
(B) 7 days
(C) 8 days
(D) 12 days
Answer:
(A) 6 days
Explanation:
The combined work rate of A and B is (1/10)+(1/15)=3/30+2/30=5/30=1/6. Therefore, working together, they will complete the work in 6 days.
39. In a library 60% of the books are in Hindi, 60% of the remaining books are in English rest of the books are in Malayalam. If there are 4800 books in English, then the total number of books in Malayalam is?
(A) 3400
(B) 3500
(C) 3100
(D) 3200
Answer:
(D) 3200
Explanation:
Let the total books be 100%. Hindi = 60%, leaving 40%. English = 60% of 40% = 24%. Malayalam = remaining 16%. If 24% equals 4800, then 1% equals 200. Thus, Malayalam books (16%) = 16×200=3200.
40. A boat travels downstream for 14km and upstream for 9km. If the boat took total of 5 hours for its journey, what is the speed of the river flow if the speed of the boat in still water is 5km/hr?
(A) 8km/hr.
(B) 2km/hr.
(C) 6km/hr.
(D) 5km/hr.
Answer:
(B) 2km/hr.
Explanation:
Let river speed be v. Time = Distance/Speed. 14/(5+v)+9/(5−v)=5. Testing the options, if v=2, then 14/(5+2)+9/(5−2)=14/7+9/3=2+3=5 hours.
