Question

can any1 hlp me figure out dis question yet?
q is ....a person moves bi car 4rm A to B ,durig journey he covers half of the distance wd speed 60 km/hr find average speed whn 1st 3rd of d rest distance wd speed 72 km /hr and d remainng distance with speed 42 km/hr.

Answer 1

first of all shruti, pls always type the full question properly as sometimes it is difficult to understand with contraction etc.....

Now let the total distance = x km
1/2 of it = x/2 and
rest distance = x/2
1/3 of rest distance = 1/3 * x/2 = x/6
final remaining = 2/3 of rest = 2/3*x/6 = 2x/18 = x/9

now time = distance/speed
so x/2
time taken for first half x/2, travelling with speed of 60 km/h = T1 = ---- = x/120 h
60
and x/6
time taken for 1/3 of rest, travelling with speed of 72 km/h = T2 = ---- = x/420 h
72

finally x/9
time taken for remaining,travelling with speed of 42 km/h = T3 = ----- = x/378 h
42

so TOTAL TIME OF THE TRIP OF x km = T1 + T2 + T3
x x x 63x + 18x + 20x 101x
= --------- + ---------- + ------- h = ----------------- = ------- h
120 420 378 7560 7560

total distance x km 7560 x
Average speed = ------------- = -------------- = --------- km/h
total time 101x/7560 h 101x

= 74.85 km/h

Answer 2

Harkirat, the process is true, but I think there is a mistake,
The last remaining distance sould be \[(2/3)*(x/2)\], so x/3 not x/9, you can verify it by summing up all the distances,
consequently, the total time should be \[(281x/15120)\]
therefore, the average speed is 53,81 km/h
( I hope I didn't commit any calculation mistake )

Answer 3

u r correct Rome, i did it yesterday night when i was dead tired, so i made the mistake u pointed out.

Thanks n u get a medal for that !!!

Answer 4

first of all shruti, pls always type the full question properly as sometimes it is difficult to understand with contraction etc.....

Now let the total distance = x km
1/2 of it = x/2 and
rest distance = x/2
1/3 of rest distance = 1/3 * x/2 = x/6
final remaining = 2/3 of rest = 2/3*x/2 = 2x/6 = x/3

now time = distance/speed
so x/2
time taken for first half x/2, travelling with speed of 60 km/h = T1 = ---- = x/120 h
60
and x/6
time taken for 1/3 of rest, travelling with speed of 72 km/h = T2 = ---- = x/420 h
72

finally x/3
time taken for remaining,travelling with speed of 42 km/h = T3 = ----- = x/126 h
42

so TOTAL TIME OF THE TRIP OF x km = T1 + T2 + T3
x x x 21x + 6x + 20x 47x
= --------- + ---------- + ------- h = ----------------- = ------- h
120 420 126 2520 2520

total distance x km 2520 x
Average speed = ------------- = -------------- = --------- km/h
total time 47x/2520 h 47x

= 53.62 km/h