Aptitude - Time and Distance - Discussion

If the answer is 224,(DISTANCE BASED).

If you think total journey 224, then half of the journey is 112 KM, travels at the speed 21 KMPH means time taken to complete 1st half is 112/21=5.33333.. hrs.

For 2nd half journey, i.e 112 KM travels at the speed 24 KMPH, the time taken for this is 112/24=4.666666...hrs.

If we add both times it will be so much near to 10 hours, but not exactly 10 hours.

If we go through following way,(TIME-BASED).its gonna be right.

Total journey is 10 hours.half of the journey is 5 hours for the 1st half journey at the speed 21 KMPH means distance travelled in 1st half is 21*5=105, in the same way, distance travelled in 2nd half is 24*5=120.

So, total distance 105+120=225km.

The easiest method is just take ratio as-

21:24=7:8(speed ratio) & sp is inversely proportion to time so 8:7(time ratio).
Now 8+7=15 portion =10hrs so 1 portion =2/3 hrs so 8 portion =16/3 hrs.
Now, dis=21*(16/3)=112(this is half dis).
So whole dis=112*2=224 km.

First half of the journey, means the first half of the distance to be travelled. Not, the first half of the time required to reach your destination! That's how it is 224 instead of 225.

I think the ans should be 225 because in first half mean in 5km he covered distance at a speed of 21kmph.

=21 * 5=105.
And in second half it mean 5km he covered distance at a speed of 24kmph =24 * 5=120.
By adding both distance=105+120=225.
Hence the ans should be 225.

average speed = 2xy/x+y.
So, 2*21*24/21+24.
2*21*24/45,
112/5=22.4.
Distance = time * speed.
= 10*22.4 =>224 kms.

How come 15? Please explain.

@Amit Kr. Soni.

Anyone please explain to me that how 7x&8x came there?

Total Time (T) = 10 hrs.
S1 = 21 kmph.
S2 = 24 kmph.
S1+ S2 = 45.
t = 45/10 = 4.5.
(2 * S1 * S2)/t.
1008/4.5 = 224km.

How this 15x arrives?

Sir, would you please explaine me the 1st line of your explanation?