M4maths Previous Puzzles

16 Oct 2012 distance

distance between X and Y station is 80 km. A train covers first half with speed 50 km/hrs and second half with speed 60 km/hrs. Calculate avg speed of the journey.

OPtion

1) 55
2) 500/11
3) 400/9
4) 500/9
5) 900/7
6) 54
7) 600/11
8) 58
9) cant be calculated
10) none of these

Solution

time taken in first part = 40/50
time taken in second part = 40/60
so total time taken = 40/50+40/60 = 40[1/50+1/60] = 40*110/3000 = 44/30
so avg speed = 80/[44/30] = 2400/44 = 600/11

Correct Option: 7 Best Solution (12)

Balakumaran N.A   12 years AGO

average speed calculation formula: 2xy/x+y
x,y are speeds of train.
so, 2*50*60 / 110 = 600/11

Like? Yes (10) | No (3)  

A J V   12 years AGO

Time= Distance / Speed;
Time = (40/50)+(40/60)
Time = 22/15

So, Speed = Distance / Time
= 80 / (22/15)
= 600 / 11

Like? Yes (4) | No   

Sri Harsha   12 years AGO

time taken to cover 1st half distance=40/50=4/5
time taken to cover 2nd half distance=40/60=2/3
total time=(4/5)+(2/3)=22/15
avg speed= total distance/total time=80/(22/15)
=1200/22=(600/11)km

Like? Yes (4) | No   

Ankush   12 years AGO

avg speed = 2*50*60/(50+60) = 600/11;

Like? Yes (5) | No (2)  

sagar arora   12 years AGO

avereage speed when the distances are equal=2xy/x+y
where x and y are speeds in different halves
so,AVG speed of whole journey is=2*50*60/110
600/11
option (7)

Like? Yes (2) | No   

Browns MN   12 years AGO

S=D/T
First Half,T=4/5hr
Second Half,T=4/6hr i,e @D=40km in each
So total time is44/30hr for 80km..Hence S=80*30/44
Which is 600/11km/hr

Like? Yes (3) | No (1)  

Prateek   12 years AGO

avg speed=2xy/x+y=(2*60*50)/(60+50)=600/11kmph-ans.

Like? Yes (1) | No   

Ankit   12 years AGO

time taken to cover first 40 km = 40/50 hr = 4/5 hr
time taken to travel last 40 km = 40/60 hr = 2/3 hr
total time taken = 22/15
average speed = 80/ ( 22/15) = 600/11

Like? Yes (2) | No (1)  

balu   12 years AGO

2xy/(x+y)
2(50)(60)/(50+60)
100*60/110
600/11

Like? Yes (1) | No   

susmit   12 years AGO

avg. speed. 2/[(1/50)+(1/60)]
=600/11

Like? Yes (1) | No (1)  

Parag Nuwal   12 years AGO

avrg speed=2xy/x+y
=(2*50*60)/(50+60)
=600/11

Like? Yes (1) | No (1)  

Manideep   12 years AGO

METHOD 1:
Using the formula Total avg speed = 2S1*S2/(s1+s2)
= 2*50*60/(50+60)
= 600/11 (OPTION 7)
Method 2:
Ratio r1:r2 = 50:60 = 5:6
r1+r2 = 11
1 part = (S2-S1)/(r1+r2) = (60-50)/11 = 10/11
Total Avg speed is r1 parts away from smaller speed
Therefore avg speed = 50+ r1*10/11 = 50+5*10/11 = 600/11(OPTION 7)

Like? Yes (2) | No (2)