Jack drove at a speed of 60km/h for 150km. He then drove the remaining 120km at a speed of 80km/h. Find his average speed for the whole journey.
Answers
Given :
Jack drove at a speed of 60km/h for 150km. He then drove the remaining 120km at a speed of 80km/h.
To find :
- Average speed for the whole journey
Solution :
- In first case
Jack drove at a speed of 60km/h for 150km
- Speed = 60km/h
- Distance (D1) = 150 km
- Time (t1) = ?
→ Time = Distance/speed
→ t1 = 150/60
→ t1 = 5/2 hours
- In second case
Jack then drove the remaining 120km at a speed of 80km/h.
- Speed = 80km/h
- Distance (D2) = 120km
- Time (t2) = ?
→ t2 = 120/80
→ t2 = 3/2 hours
Average speed for the whole journey
★ Total distance travelled/total time taken
→ D1 + D2/t1 + t2
→ 150 + 120/5/2 + 3/2
→ 270/5 + 3/2
→ 270/8/2
→ 270 × 2/8
→ 270 × 1/4
→ 67.5 km/h
•°• Average speed for whole journey is 67.5 km/h
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Answer:
Given :-
- Jack drove at a speed of 60 km/h for 150 km. He then drove the remaining 120 km at a speed of 80 km/h.
To Find :-
- What is the average speed for the whole journey.
Formula Used :-
✪ Time = Distance/Speed ✪
✯ Average Speed = Total Distance/Total time ✯
Solution :-
In first case :-
Given :
- Speed (s) = 60 km/h
- Distance (d₁) = 150 km
According to the question by using the formula we get,
⇒ Time (t₁)= 150/60
⇒ Time (t₁) = 15/6
➠ Time (t₁) = 5/2 hrs
In second case :-
Given :
- Speed = 80 km/h
- Distance (d₂) = 120 km
According to the question by using the formula we get,
⇒ Time (t₂) = 120/80
⇒ Time (t₂) = 12/8
⇒ Time (t₂) = 6/4
➠ Time (t₂) = 3/2 hrs
Now, we have to find the average speed for the whole journey,
Given :
- d₁ = 150 km
- d₂ = 120 km
- t₁ = 5/2 hrs
- t₂ = 3/2 hrs
According to the question by using the formula we get,
↦ Average Speed = 150 + 120/5/2 + 3/2
↦ Average Speed = 270/8/2
↦ Average Speed = 270 × 2/8
↦ Average Speed = 270 × 1/4
➦ Average Speed = 67.5 km/h
∴ The average speed for the whole journey is 67.5 km/h .