Help with a Physics speed/time problem?

Question

Problem: An airplane travels 2100 km at a speed of 800 km/hr, and then encounters a tailwind that boosts its speed to 1000 km/hr for the next 1800 km. What was the total time for the trip? What was the average speed of the plane for this trip?

I came up with a solution for the first part:

2100km * hr/800km = 2.625 hr

1800km * hr/1000km = 1.8 hr

total time = 2.625 hr + 1.8 hr = 4.425 hr

However, I'm not sure how I should go about solving the second part of the problem. Any help would be greatly appreciated.

Answer 1

You're doing well

Your answer is correct but you typed it incorrectly

t1=x1/v1=2100/800=2.625 hr

t2=x2/v2=1800/1000=1.8 hr

and the total time is exactly as the number you got

For the second part

Average speed = 2/(1/v1 + 1/v2)= 2÷9/4000 =889 km/hr

Undoubtedly you know these symbols but I just put it to take precautions

v1 is 1st velocity

v2 is 2nd velocity

t1 is 1st period of time (during moving with v1)

t2 is 2nd period of time (during moving with v2)

x1 is the distance the plane crossed  (during moving with v1 in t1)

x1 is the distance the plane crossed  (during moving with v1 in t1)

x2 is the distance the plane crossed  (during moving with v2 in t2)

Answer 2

The average velocity,

V = Total distance travelled/total time travelled

V = (2100 + 1800)/(2.625 + 1.8)

V = 3900/4.425

V = 881.36 km/hr.

Answer 3

average speed=distance/time

average speed=(2100+1800)/(2.625+1.8)

avg speed=881.4 km/h

Don't listen to the other guys, I'm 95% confident that I am right.