Final answer:
To find out how long it will take for Mary and Janet to be 1.5 miles apart, we calculate the relative speed at 2 mph and then divide the distance by the relative speed, giving us 0.75 hours or 45 minutes.
Step-by-step explanation:
In this problem, we are dealing with a situation where Mary and Janet are running at different constant speeds and we need to determine how long it will take for them to be a certain distance apart. Since they start at the same time, we can use the concept of relative speed to solve the problem.
The relative speeds of Mary and Janet the different in their speeds because they are moving in the same direction. So, the relative speed is:
Relative speed = Speed of Mary - Speed of Janet = 7 mph - 5 mph = 2 mph.
Since we are asked to find out when they will be 1.5 miles apart, we use the formula:
Time = Distance / Relative Speed
So, Time = 1.5 miles / 2 mph = 0.75 hours.
To convert hours into minutes, we multiply by 60:
Time in minutes = 0.75 hours x 60 minutes/hour = 45 minutes.
Therefore, Mary and Janet will be 1.5 miles apart after 45 minutes.