Question

On his outward journey, Ali travelled at a speed of s km/h for 2.5 hours. On his return journey, he increased his speed by 4 km/h and saved 15 minutes. Find Ali's average speed for the whole journey.

Answer 1

Answer:

3.08 km/h.

Step-by-step explanation:

We know that,

$Speed=\dfrac{Distance}{Time}$

Ali traveled at a speed of s km/h for 2.5 hours.

Let d be the distance and t be the time.

$2.5=\dfrac{d}{t}$

$2.5t=d$      ...(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.

$4=\dfrac{d}{t-15}$

$4(t-15)=d$      ...(2)

From (1) and (2), we get

$4(t-15)=2.5t$

$4t-60-2.5t=0$

$1.5t=60$

$t=40$

Put t=40 in (1).

$d=2.5(40)=100$

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

$\text{Average speed}=\dfrac{\text{Total distance}}{\text{Total time}}$

$\text{Average speed}=\dfrac{200}{65}$

$\text{Average speed}\approx 3.08$

Therefore, the average speed is 3.08 km/h.