Question

David drove the first 6 hours of his journey at 65 km / hour and the last 3 hours of his journey at 80 km / hour . How far is the whole journey in km ?

Answer 1

Answer:

630 km.

Explanation:

To obtain the total distance travelled by David, we shall calculate the distance travelled in each, then sum them together.

Case 1:

Speed 1 (S₁) = 65 km / hour

Time 1 (t₁) = 6 hours

Distance 1 (d₁) =?

Speed = Distance /time

S₁ = d₁ / t₁

65 = d₁ / 6

Cross multiply

d₁ = 65 × 6

d₁ = 390 Km

Case 2:

Speed 2 (S₂) = 80 km / hour

Time 2 (t₂ ) = 3 hours

Distance 2 (d₂) =?

Speed = Distance /time

S₂ = d₂ / t₂

80 = d₂ / 3

Cross multiply

d₂ = 80 × 3

d₂ = 240 Km

Finally, we obtained the total distance travelled by David as follow

Distance 1 (d₁) = 390 Km

Distance 2 (d₂) = 240 Km

Total Distance travelled (dₜ) =?

Total distance = distance 1 + distance 2

dₜ = d₁ + d₂

dₜ = 390 + 240

dₜ = 630 km

Therefore, the total distance travelled by David is 630 km