Respuesta :
Answer:
3.08 km/h.
Step-by-step explanation:
We know that,
[tex]Speed=\dfrac{Distance}{Time}[/tex]
Ali traveled at a speed of s km/h for 2.5 hours.
Let d be the distance and t be the time.
[tex]2.5=\dfrac{d}{t}[/tex]
[tex]2.5t=d[/tex] ...(1)
On his return journey, he increased his speed by 4 km/h and saved 15 minutes. So, distance is d and times is t-15.
[tex]4=\dfrac{d}{t-15}[/tex]
[tex]4(t-15)=d[/tex] ...(2)
From (1) and (2), we get
[tex]4(t-15)=2.5t[/tex]
[tex]4t-60-2.5t=0[/tex]
[tex]1.5t=60[/tex]
[tex]t=40[/tex]
Put t=40 in (1).
[tex]d=2.5(40)=100[/tex]
So, t=40 and d=100.
Now,
Total distance = d + d = 100 + 100 = 200
Total time = t + t - 15 = 40 + 40 - 15 = 65
So, the average speed is
[tex]\text{Average speed}=\dfrac{\text{Total distance}}{\text{Total time}}[/tex]
[tex]\text{Average speed}=\dfrac{200}{65}[/tex]
[tex]\text{Average speed}\approx 3.08[/tex]
Therefore, the average speed is 3.08 km/h.
