1. A thief is spotted by a policeman from a distance of 100 m. When the policeman starts the chase, the thief also starts running. If the speed of the thief be 8 km/hr and that of the policeman 10 km/hr. How far the thief will have run before he is overtaken?
A. 100 m
B. 150 m
C. 200 m
D. 400 m
Answer: Option D
Explanation:
Realtive speed of policeman = (10 – 8) km/hr = 2 km/hr.
Time =[latex]\frac{Distance}{Speed}[/latex]
Time taken by policeman to cover 100 m
= ([latex]\frac{100}{1000}[/latex]* [latex]\frac{1}{2}[/latex])hr= [latex]\frac{1}{20}[/latex]hr
In [latex]\frac{1}{20}[/latex]hr the thief covers a distance of
= (8*[latex]\frac{1}{20}[/latex])= 400m.
2. I walk a certain distance and ride back taking a total time of 37 minutes. I could walk both ways in 55 minutes. How long would it take me to ride both ways?
A. 5 min.
B. 10 min.
C. 13 min.
D. 19 min.
Answer: Option D
Explanation:
Let the distance be x, then,
(Time taken to walk x km) + (Time taken to ride x km) = 37min.
⇒ (Time taken to walk 2x km) + (Time taken to ride 2x km) = 74 min.
But, time taken to walk 2x km = 55 min.
So, Time to ride 2x km = (74 - 55) min ⇒ 19 min.
Hence, option D is correct.
3. A motor-cycle covers 40 km with a speed of 20 km/hr. find the speed of the motor-cycle for the next 40 km journey so that the average speed of the whole journey will be 30 km/hr.
A. 70 km/hr
B. 52.5 km/hr
C. 60 km/hr
D. 60.5 km/hr
Answer: Option C
Explanation:
Average speed of whole journey = 30 km/hr
x = speed of first 40 km = 20 km/hr
30= [latex]\frac{2 * 20 * y}{20 + y}[/latex]
600 + 30y = 40y ⇒ 10y = 600
y= [latex]\frac{600}{10}[/latex]= 60 km/hr
4. A man rides at the rate of 18 km/hr, but stops for 6 minutes to change horses at the end of every 7th km. The time that he will take to cover a distance of 90 km is
A. 6 hrs
B. 6 hrs. 12 min.
C. 6 hrs. 18 min.
D. 6 hrs. 24 min.
Answer: Option B
Explanation:
Number of stoppages
= [latex]\frac{90}{7}[/latex]= 12.8,
it means there is 12 stoppages.
Distance to be covered = 90 km, Speed = 18,
Time for each stoppage = 6 mins.
By the short trick approach, we get
= [latex]\frac{90}{18}[/latex] + 12 * 6
5 hrs + 72 mins
Convert mins to hours then,
= 6 hrs 12 mins.
5. Walking at 3 km/hr . Pintu reaches his school 5 minutes late. If he walks at 4 km per hour he will be 5 minutes early. The distance of Pintu’s from his house is
A. 1[latex]\frac{1}{2}[/latex]km
B. 2 km
C. 2[latex]\frac{1}{2}[/latex]km
D. 5km
Answer: Option B
Explanation:
Speed1 = 3 km/hr, Speed2 = 4 km/hr
Time1 = 5 mins late, Time2 = 5 min early
Reqd. Distance
[latex]\frac{3 * 4}{4 – 3}[/latex] * [latex]\frac{5 + 5}{60}[/latex]= 2 km