56.	Jennie Blekping mengendarai sebuah motor dengan kecepatan 45 km/ jam. Setelah lima jam, motor tersebut melaju dengan kecepatan 60 km/ jamjika kecepatan rata-rata motor selama perjalanan adalah 50 km/ jam maka lamanya perjalanan tersebut adalah
a.	2,3 jam
b.	7,5 jam
c.	6,5 jam
d.	9 jam
e.	10 jam


To determine the total time of the journey, we can use the concept of average speed. 

Given:
- First part of the journey: 45 km/h for 5 hours.
- Second part of the journey: 60 km/h.
- Average speed of the entire journey: 50 km/h.

First, calculate the distance traveled during the first part of the journey:
\[ \text{Distance}_1 = \text{Speed}_1 \times \text{Time}_1 \]
\[ \text{Distance}_1 = 45 \text{ km/h} \times 5 \text{ hours} = 225 \text{ km} \]

Next, let \( t \) be the time taken for the second part of the journey.

The distance traveled during the second part of the journey is:
\[ \text{Distance}_2 = \text{Speed}_2 \times t \]
\[ \text{Distance}_2 = 60 \text{ km/h} \times t \]

The total distance is the sum of the distances traveled in both parts:
\[ \text{Total Distance} = \text{Distance}_1 + \text{Distance}_2 \]
\[ \text{Total Distance} = 225 \text{ km} + 60t \text{ km} \]

Given that the average speed for the entire journey is 50 km/h, the total time for the journey is:
\[ \text{Total Time} = 5 \text{ hours} + t \]

The average speed can be expressed as:
\[ \text{Average Speed} = \frac{\text{Total Distance}}{\text{Total Time}} \]
\[ 50 = \frac{225 + 60t}{5 + t} \]

Now, solve for \( t \):
\[ 50(5 + t) = 225 + 60t \]
\[ 250 + 50t = 225 + 60t \]
\[ 250 - 225 = 60t - 50t \]
\[ 25 = 10t \]
\[ t = 2.5 \text{ hours} \]

Thus, the total time for the journey is:
\[ \text{Total Time} = 5 \text{ hours} + 2.5 \text{ hours} = 7.5 \text{ hours} \]

Therefore, the correct answer is:
\[ b. 7.5 jam \]

Would you like more details or have any questions? Here are 5 more questions you might find interesting:
1. How do you calculate the average speed of a journey?
2. What is the difference between average speed and instantaneous speed?
3. How do you solve a quadratic equation?
4. What are the different methods to find the roots of a polynomial?
5. How do you apply the Pythagorean theorem in real-world problems?

Tip: Always check your units to ensure they are consistent throughout the problem.

Learn how to calculate the total time of a journey using average speed and distance-time relationships. This math problem involves determining the journey's total time based on varying speeds over different periods. Suitable for Grades 7-9.

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