A bus covers 30% of a journey at a speed of 24 km/h and the remaining distance at a speed of 36 km/h. What is the average speed of the bus for the entire journey?

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- **Step 1:** Let total distance be $D$. Time for first part (30%) = $\dfrac{0.3D}{24}=\dfrac{D}{80}$.  
- **Step 2:** Time for remaining part (70%) = $\dfrac{0.7D}{36}=\dfrac{7D}{360}$.  
- **Step 3:** Total time = $D\left(\dfrac{1}{80}+\dfrac{7}{360}ight)=D\cdot\dfrac{23}{720}$.  
- **Step 4:** Average speed $=\dfrac{D}{	ext{time}}=\dfrac{D}{D\cdot 23/720}=\dfrac{720}{23}\approx 31.3	ext{ km/h}$.  
- **Conclusion:** Choice (d) is correct.  
FINAL_ANSWER: d

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