My friend sets out walking at a speed of 3 miles per hour. I set out behind her 5 minutes later at 5 miles per hour. For how many minutes will my friend have been walking when I catch up to her?
Let the time it takes you to catch up to your friend==T
5T ==3 [T + 5], solve for T
5T ==3T + 15
5T - 3T ==15
2T == 15
T ==15 / 2 ==7.5 minutes -for you to catch up to her
7.5 + 5 ==12.50 minutes - your friend had been walking when you caught up to her.