Question:

A car driver increases the average speed of his car by 3 km/hr every hour. The total distance travelled in 7 hours if the distance covered in first hour was 30 km, is

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When speed (or distance per hour) increases by a fixed amount each hour, use the sum of an AP: $S_n=\frac{n}{2}[2a+(n-1)d]$.
Updated On: Aug 13, 2025
  • 266 km
  • 273 km
  • 280 km
  • 287 km
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The Correct Option is B

Solution and Explanation

Distance covered each hour forms an arithmetic progression:
First hour $=30$ km; common difference $=3$ km.
Seven hourly distances: $30,33,36,39,42,45,48$.
Sum of AP: $S_n=\dfrac{n}{2}\,[2a+(n-1)d]$.
$S_7=\dfrac{7}{2}\,[2\cdot30+(7-1)\cdot3]=\dfrac{7}{2}\,(60+18)=\dfrac{7}{2}\times78=273$ km.
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