Discussion
A car started running at a speed of 30 km/hr and the speed of the car was increased by 2 km/hr at the end of every hour. Find the total distance covered by the car in the first 10 hours of the journey.
Answer: B
The hourly distances form an arithmetic progression: 30, 32, 34, … with \( a = 30 \), \( d = 2 \) and \( n = 10 \).
\[ S_{n} = \frac{n}{2}\left[2a + (n-1)d\right] \]
\[ = \frac{10}{2}\left[60 + 9 \times 2\right] = 5 \times 78 = 390 \text{ km} \]
Multiplying the first hour's 30 km by 10 would give 300 km, ignoring the acceleration entirely.
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