11. A train leaves a station A at 5 am. And reaches B at 9 a.m. Another train leave B at 6 : 30 am and reaches A at 10 am on the same day. On parallel tracks. They will meet each other at
A. 7 : 40 a.m
B. 7 : 50 a.m
C. 8 : 40 a.m
D. 8 : 50 a.m
Answer: Option A
Explanation:
[latex]{T}_{1} : {T}_{2} [/latex] = 4 : 3.5
[latex]{V}_{1} : {V}_{2} [/latex] = 3.5 : 4
Let total distance = 4 × 3.5x
Distance covered by train 1 till 6 : 30 am = 1.5 × 3.5x
i.e, Meeting time[latex]\frac {Distance left}{Relative speed} [/latex] = [latex]\frac {14x - 5.25x}{75x} [/latex]
= 1.16 hours
i.e 7 : 40 am
12. A person can row 9 km/hour in still water and he finds that it takes him twice as much time to row upstream as to row downstream the same distance. The speed of the current, in km/hour, is
Answer: Option B
Explanation:
speed in still water = 9 km/ pr
Time up : Time Down = 2 : 1
i.e,speed up : speed Down = 1 : 2
speed in still water = [latex]\frac {1}{2}[/latex](x ÷ 2x) = 9
x = 6 km/ pr
speed of current = [latex]\frac {1}{2}[/latex](2x - x) = 3
13. Anu travel by car and covers [latex]\frac{1}{4}[/latex]th of her journey with a speed of 60 km/hour, 40% her journey with a speed of 50 km/hour, and the rest with a speed of 42 km/hours. The average speed (km/hour) for the whole journey is about
A. 46.8
B. 48.8
C. 49.7
D. 50.1
Answer: Option B
Explanation:
Distance = [latex] x\frac {1 } {4} + x\frac {2} {5} + x\frac {35} {100}[/latex]
Time = [latex] \frac {x} {4 * 60} + \frac {2x} {5 * 50} + \frac {35x} {100 * 42}[/latex]
i.e, Avg speed = [latex] \frac {Total Distance} {Total Time}[/latex] = 48.8km / pr
14. Two places A and B are 220 km apart on a highway Hari starts from A and Juhi from B at the same time on the same day using cars. If they travel in the same direction (A to B ), hey meet in 5 [latex]\frac {1} {2}[/latex] hour s, but in 2 hour s 45 mi nut es when travelling towards each other. Speed of the car of Juhi, in km/hour, is
Answer: Option A
Explanation:
Let speed of A be x km/hr
let speed of B be y km/hr
[latex]\frac {220} {x - y}[/latex] = [latex] 5 \frac {1} {2}[/latex] = [latex]\frac {11} {2}[/latex]
[latex]\frac {220} {x + y}[/latex] = [latex] 2 \frac {3} {4}[/latex] = [latex]\frac {11} {4}[/latex]
x = 60 km/hr
y = 20 km/hr
= 20 km/hr
15. A covers a certain distance in a certain time, if B covers half of this distance in the double time, the ratio of speeds of A and B is
A. 2 : 1
B. 4 : 1
C. 1 : 2
D. 1 : 4
Answer: Option B
Explanation:
According to question, [latex]\frac {D} {{S}_{A}}[/latex]
[latex]\frac {\frac {D}{2}} {{S}_{B}}[/latex]
[latex] {S}_{A} : {S}_{B}[/latex] = 4 : 1