Question

Kate cycle the first 350 km of a 470-km journey at a certain avearge speed and the remaining distanceat an average that is 15km/h less than that for the first part of the journe. If the time taken for her to travel each part for her to travel each part of her journey is the same, find the average speed for the second part of her journey

Answer 1

7.83 km/h

Explanation:

Let v = average speed for first part, v' = average speed for second part.

Given that v' = v - 15, the distance covered by the first part d = 350 km. The distance covered in the second part d' = 470 km - 350 km = 120 km.

Since both parts are covered in the same time,

d = vt and d' = v't = (v - 15)t

So, 350 = vt (1) and 120 = vt - 15t (2)

substituting vt = 350 into (2), we have

120 = 350 - 15t

collecting like terms, we have

15t = 350 - 120

simplifying, we have

15t = 230

dividing through by 15, we have

t = 230/15

t = 15.33 h

Since d' = v't, then

v' = d'/t

= 120 km/15.33 h

= 7.83 km/h

So, the average speed for the second part of the journey is 7.83 km/h