Question : If a truck moves at a constant speed of 30 km/hr for 1 kilometre and 45 km/hr for the next 1 kilometre. What is the average speed of the truck?
Option 1: 32 km/hr
Option 2: 36 km/hr
Option 3: 38 km/hr
Option 4: 34 km/hr
Correct Answer: 36 km/hr
Solution :
Total distance covered in 2 km/hr.
The time taken for the first kilometre at 30 km/h = $\frac{1}{30}$ hours
The time taken for the second kilometre at 45 km/h = $\frac{1}{45}$hours
Total Time taken :
= $\frac{1}{30}$ + $\frac{1}{45}$
Now using the average speed formula:
⇒ Average speed = $\frac{\text{Total Distance}}{\text{Total Time}}$ = $\frac{2}{\frac{3}{90} + \frac{2}{90}}$ = $\frac{2}{\frac{5}{90}}$ = $\frac{2 × 90}{5}$ = $\frac{180}{5}$ = 36 km/hr
Hence, the correct answer is 36 km/hr.
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