An airplane flies at 800km/h for one-third of its flight and averages 700km/h for the rest. What is the average speed, in km? Show working?

The average speed
= 800 × (1/3) + 700 × (2/3) km/h
= 733 and (1/3) km/h

(The unit of speed is km/h, but not km.)

UPDATE:
I kinda got the answer without you guys. It was 650km/h. Check what you did wrong or how you did it.

distance = speed * time
apply to whole trip and each part

let:
total time be T
total distance be D = D1+D2

D1 = 800*T(1/3)
D2 = 700*T(2/3)

average speed (s) = D/T
= [800*T(1/3)+700*T(2/3)]/T

T cancels out
s = 800(1/3)+700(2/3) = 2200/3
= 733 1/3 km

Recall: s = d/t → where s is the speed, d is the distance, t is the time


The airplane flies at 800 km/h for one-third of its flight.

s₁ = d₁/t₁

d₁ = s₁ * t₁ → given that: s₁ = 800

d₁ = 800 * t₁


The airplane flies at 700 km/h for the rest of its flight.

s₂ = d₂/t₂

d₂ = s₂ * t₂ → given that: s₂ = 700

d₂ = 700 * t₂


s = (total distance) / (total time) ← where the total time of the trip is t

s = (d₁ + d₂) / (t₁ + t₂)

s = [(800 * t₁) + (700 * t₂)] / t

s = [800.(1/3).t + 700.(2/3).t] / t

s = [(800/3).t + (1400/3).t] / t

s = (800/3) + (1400/3)

s = 2200/3

s ≈ 733.33 km/h

Let length of flight = x km
t1 = x/3 / 800 h = x / 2400 h
t2 = 2x/3 / 700 h = 2x / 2100 h

t = x / 2400 h + x / 1050 h

t = [ 1050 + 2400 ] x / 2520000 h
t = 3450 x / 2520000 h

speed = 2520000 / 3450 km / h = 730 • 4 km/h

An airplane flies at 800 km/h for one-third of its flight and
averages 700 km/h for the rest.
The average speed is (800/3 + 2(700)/3) or 733 1/3 km/h.