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In a potato race at a school sports day, a bucket is placed at the start. The first potato is 6 m from the bucket and the 8 potatoes are 4 m apart in a straight line. A runner fetches one potato at a time and drops it in the bucket. What total distance does she run?

Class 10Arithmetic ProgressionsAlgebra — Sequences
  • A160 m
  • B320 m
  • C288 m
  • D68 m

Step-by-Step Solution

Distances to the potatoes are 6, 10, 14, …, 34 m. Each trip is there and back: m.
Answer: B) 320 m

Key idea: Sum of first n terms

**Sₙ = []**

Or equivalently, **Sₙ = **, where is the LAST term (the n-th term).

**Why these are equal**: , so .

**Example**: Sum of 1, 4, 7, …, 28.
First find . From aₙ = 28: → .
Then S₁₀ = .

**Special case natural numbers)**: Sₙ = .
**First odd numbers**: Sₙ = .
**First even numbers**: Sₙ = .

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