ROHIT11111 wrote:10. A lorry sets off at 06.00 to make a delivery 220 kilometres away at 10.00 At 06.56, 50 kilometres have been covered. During the next hour the lorry travels at an average speed of 56 kilometres per hour, followed by a further 30 kilometres at 72 kilometres per hour. If the lorry is to arrive on time, what must be its average speed for the remainder of the journey? (Express your answer to 2 decimal places).

ans-50.91km per hr

Hi ROHIT11111,

I see that you have posted a number of questions that are not GMAT like. It is highly unlikely that you will get such calculation intensive question on the GMAT. If you get a question testing these concepts, then the options would not want you to calculate till second place.
It is very tempting to believe that the more you practice, the better you become. But unfortunately, if you practice from random sources, you will do yourself no good.

Coming back to the question,

Information given:

Desired average speed = 220/4 = 55 km/hr
50 kms travelled in 56 minutes.
56 kms travelled in next 60 minutes

30 kms travelled in (30/72)*60 = 25 minutes.

Total distance covered = 136 km, Distance left = 220 - 136 = 84 km
Total time elapsed = 141 minutes, Time left = 240 - 141 = 99 minutes.

Required average speed = 84 / (109/60) = 84*60/99 km/hr = 50.91 km/hr