Answer:
Joan drive with a speed of 55 miles per hour.
Step-by-step 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 = ![\frac{distance}{time}](https://tex.z-dn.net/?f=%5Cfrac%7Bdistance%7D%7Btime%7D)
-------------(from 1 and given)
![2x+10=120](https://tex.z-dn.net/?f=2x%2B10%3D120)
![2x=120-10](https://tex.z-dn.net/?f=2x%3D120-10)
![2x=110](https://tex.z-dn.net/?f=2x%3D110)
![\therefore x=\frac{110}{2}](https://tex.z-dn.net/?f=%5Ctherefore%20x%3D%5Cfrac%7B110%7D%7B2%7D)
![\therefore x= 55](https://tex.z-dn.net/?f=%5Ctherefore%20x%3D%2055)
as x is the speed of Joan,
Therefore Joan drive with a speed of 55 miles per hour.