Question 630854
Let the younger sister's speed be x. The older sister travels at three times the speed ie at 3x.
In 5 hours the younger sister travels 5x miles and the older sister travels 5 times 3x = 15x miles.
the total distance travelled by the two girls is 5x + 15 x = 20x
ie 20x = 20 so x = 1
The younger sister is travelling at 1 mile per hour and the older sister travels at 3 miles per hour.