Ex 5.3, 13 - Find the sum of first 15 multiples of 8. - Ex 5.3

  1. Chapter 5 Class 10 Arithmetic Progressions
  2. Serial order wise
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Ex 5.3 ,13 Find the sum of first 15 multiples of 8. Multiples of 8 are 8, 16, 24,… Since difference is same, it is an AP We need to find sum of first 15 multiples We use formula Sn = 𝑛/2 (2𝑎+(𝑛−1)𝑑) Here, n = 15, a = 8 & d = 16 – 8 = 8 Putting values in formula Sn = 𝑛/2 (2𝑎+(𝑛−1)𝑑) = 15/2(2×8+(15−1)×8) = 15/2 (16+14×8) = 15/2 (16+112) = 15/2×128 = 960 Therefore, the sum of first 15 multiples of 8 is 960

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