Question

Joan and her brother Justin left a hotel at the same time, driving in opposite directions at constant rates. After traveling for 4 hours, they were 480 miles apart. If Justin drove 10 miles per hour faster than Joan, how fast did Joan drive?

Answer 1

Joan drive with a speed of 55 miles per hour.

Explanation:

Given:- Travelling time (t) = 4 hours.

Travelled distance (d) = 480 miles.

Speed of Justin is 10 miles per hour faster than Joan.

To find:- Speed of Joan = ?

Solution:-

Let speed of Joan be x,

therefore speed of Justin = x+10 ---------------(from given)

Now, Total speed of Joan and Justin = x+x+10

Total speed of Joan and Justin = 2x+10 ------------(1)

Now formula for speed is,

Speed =
`(distance)/(time)`

`2x+10=(480)/(4)` -------------(from 1 and given)

`2x+10=120`

`2x=120-10`

`2x=110`

`\therefore x=(110)/(2)`

`\therefore x= 55`

as x is the speed of Joan,

Therefore Joan drive with a speed of 55 miles per hour.