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A train covers the first 16 km at a speed of 20 km per hour another 20 km at 40 km per hour and the last 10 km at 15 km per hour. Find the average speed for the entire journey.
Answer & Solution
Correct Answer:
Option
D
$$\eqalign{
& {\text{Average}}\,{\text{speed}} \cr
& = \frac{{{\text{total}}\,{\text{distance}}\,{\text{covered}}}}{{{\text{total}}\,{\text{time}}}} \cr
& {\text{Total}}\,{\text{Distance}} \cr
& = {16 + 20 + 10} \cr
& = 46\,{\text{km}} \cr
& {\text{Time}}\,{\text{taken}} \cr
& = {\frac{{16}}{{20}}} + {\frac{{20}}{{40}}} + {\frac{{10}}{{15}}} \cr
& = {\frac{{4}}{{5}}} + {\frac{{1}}{{2}}} + {\frac{{2}}{{3}}} \cr
& = {\frac{{24 + 15 + 20}}{{30}}} \cr
& = \frac{{59}}{{30}} \cr
& {\text{Average}}\,{\text{speed}} \cr
& = \frac{{46 \times 30}}{{59}} \cr
& = 23\frac{{23}}{{59}}\,{\text{km/hr}} \cr} $$
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LoginDistance = 16 km.
speed = 20 km/hr .
Time = Distance/speed .
16/20 = 4/5 hrs
▶ 2nd journey :-
Distance = 20 km.
speed = 40 km/hr.
Time = Distance/Speed
20/40 =1/2 hrs
▶3rd journey :-
Distance = 10 km.
Time = 15 km/hr .
Time = Distance/Speed
10/15 =2/5
➡ Now,
avrg= total distance travelled/total time =2323/59
Can you explain please
After this for 4/5we multiply it with the bottom numbers 2 and also from 3 we get 4*2*3i.e24
So 24/5 next for 1/2 we multiply it with the bottom numbers 5and 3i. e, 5*3*1=15 so 15/2 and DJ or 2/3 we multiply it with the bottom numbers 5and 2 I. e, 20/3 now multiply all the bottom numbers I. e, 5*2*3=30 so atlast we get the answer 24+15+20/30
By adding 24+15+30 we get 59 which is divided by 30 hence we get 59/30
???????????????
how 46*30/59 = 23(23/59) ????
Can you please explain?