Deconstructing the QuestionHarriet makes a round trip (A to B and back to A).
This means the
Distance is Constant.
We are given the total time (5 hours) and the two speeds. The most efficient way to solve this is using the
Ratio Method to avoid complex fractions.
- Speed A to B (\(S_1\)): 115 km/h
- Speed B to A (\(S_2\)): 135 km/h
- Total Time: 5 hours (300 minutes)
Step 1: Establish the RatiosFirst, find the ratio of the speeds and simplify it.
\(S_1 : S_2 = 115 : 135\)
Divide both sides by 5:
\(S_1 : S_2 = 23 : 27\)
Since Distance is constant, Time is
inversely proportional to Speed.
\(T_1 : T_2 = 27 : 23\)
Step 2: Determine the Value of the Ratio UnitsThe total trip consists of \(27 + 23 = 50\) "units" of time.
We know the actual total time is 5 hours, which is \(5 \times 60 = 300\) minutes.
Equating the units to real time:
\(50 \text{ units} = 300 \text{ minutes}\)
\(1 \text{ unit} = \frac{300}{50} = 6 \text{ minutes}\)
Step 3: Calculate the Specific Time RequestedThe question asks for the time to drive from
A-ville to B-town (the first leg).
Based on our inverted ratio, \(T_1\) corresponds to
27 units.
\(Time_{A \to B} = 27 \text{ units} \times 6 \text{ minutes/unit}\)
\(Time_{A \to B} = 162 \text{ minutes}\)
Answer: D