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Course: Class 10 > Unit 3

Lesson 4: Sum of first n terms of an AP
Math
Class 10
Arithmetic progressions
Sum of first n terms of an AP
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Sum of n terms (advanced)

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Problem

The sum of the first 6 terms of an arithmetic progression is 138.
The 9th term and the 14th term are the ratio 9:13.
Find the first term, a1.
a1=
  • Your answer should be
  • an integer, like 6
  • a simplified proper fraction, like 3/5
  • a simplified improper fraction, like 7/4
  • a mixed number, like 1 3/4
  • an exact decimal, like 0.75
  • a multiple of pi, like 12 pi or 2/3 pi