Safety regulations require that the time between airplane takeoffs (on the same runway) will be at least 2 minutes. When taking off, the run time of an airplane on the runway is 27 seconds. Planes are on average waiting 4 minutes and 21 seconds for take-off. On average there are 21 planes taking off per hour. How many planes are either on the runway or waiting to take off

Number of planes on the runway or waiting to take off is approximately 2

Step-by-step explanation:

Given the data in the question;

On average there are 21 planes taking off per hour

rate of flow = frequency of take off = 21 planes / hr

= 21 planes per 60 minutes

= 0.35 planes/min

Now, we get the throughput time

throughput time = total time for take off =  waiting time on runway + run time on runway

= (4 minutes and 21 seconds) + 27 seconds

= 4.35 minutes + 0.45 minutes

= 4.8 minutes

Now, using Little's law;

Number of planes on the runway or waiting to take off will be;

N = Rate of flow × throughput time

we substitute

N = ( 0.35 planes/min ) × 4.8 min

N = 1.68 planes ≈ 2 planes

Therefore, Number of planes on the runway or waiting to take off is approximately 2

three-fourths of an hour

36÷48=0.75

0.75=