Question

In a race from point X to point Y and back, Jack averages 30 miles per hour to point Y and 10 miles per hour back to point X. Sandy averages 20 miles per hour in both directions. Between Jack and Sandy, who finished first?

Answer 1

Sandy will finish the race first.

Explanation:

Let D be the total one sided distance in miles, ( between X and Y ),

We know that,

`Speed =(Distance)/(Time)`

`\implies Time =(Distance)/(Speed)`

Since, from point X to point Y and back, Jack averages 30 miles per hour to point Y and 10 miles per hour back to point X.

So, the total time taken by Jack =
`(D)/(30)+(D)/(10)`

`=(D+3D)/(30)`

`=(4D)/(30)`

`=0.1333D`

Also, Sandy averages 20 miles per hour in both directions,

So, the total time taken by Sandy =
`(D)/(20)+(D)/(20)`

`=(D+D)/(20)`

`=(2D)/(20)`

`=(D)/(10)`

`=0.10D`

∵ 0.133D > 0.10D

Hence, Sandy will finish the race first.