Victoria and margaret left their apartment at the same time traveling in the same direction. Victoria drove at 55 mph and Margaret drove at 70 mph. How many hours was it before Margaret was 30 miles ahead of Victoria?
In word problems, first seek what data was given and what is the question:
Question: How many hours before Margaret was 30 miles ahead of Victoria = h
Victoria's speed = 55mph
Margaret's speed = 70mph
They drove in the same direction (an important thing to think about for speed/time/distance problems with two characters).
The formula for speed is rate = distance/time
A related formula for time = distance/rate
We want to find the time h. We know the speeds but we don't know the distance. Because we are asked the time when Margaret was 30 miles ahead of Victoria, we can consider Victoria's distance is d and Margaret's distance is d + 30.
With this information, we can plug in the formulas:
Victoria h = d/55
Margaret h = (d + 30)/70
Because the question is asking for the same amount of time concerning both Victoria and Margaret, the h in both equations are equal. Therefore we can use substitution and substitute one of the hs with its value from the other equation.
d/55 = (d + 30)/70 This is in the form of a proportion so we can cross multiply.
70d = 55(d + 30) Eliminate parenthesis by distributive property.
70d = 55d + 1650 Subtract 55d from both sides.
15d = 1650 Divide both sides by 15
d = 110
Now that we have found Victoria's distance, we can plug that value in to determine the time h.
h = d/55
h = 110/55
h = 2
It took 2 hours for Margaret get 30 miles ahead of Victoria.