web analytics

Ex 5.3, 8 - Find sum of first 51 terms of an AP whose second - Determining AP and finding sum

  1. Chapter 5 Class 10 Arithmetic Progressions
  2. Serial order wise
Ask Download

Transcript

Ex 5.3 ,8 Find the sum of first 51 terms of an AP whose second and third terms are 14 and 18 respectively. We know that an = a + (n – 1) d From (1) & (2) 14 – d = 18 – 2d 2d – d = 18 – 14 d = 4 Putting value of d in (1) a = 14 – d a = 14 – 4 a = 10 Now, we need to find sum of first 51 terms We can use formula Sn = 𝑛/2 (2 a + (n – 1) d) Here , n = 51 , a = 10 & d = 4 Putting values Sn = 𝑛/2 (2a + (n – 1) d) S51 = 51/2 (2 ×10+(51−1)×4) S51 = 51/2 (20 + 50×4) S51 = 51/2×(20+200) S51 = 51/2×220 S51 = 51 × 110 S51 = 5610 Hence the sum of first 51 terms is 5610

About the Author

CA Maninder Singh's photo - Expert in Practical Accounts, Taxation and Efiling
CA Maninder Singh
CA Maninder Singh is a Chartered Accountant for the past 8 years. He provides courses for Practical Accounts, Taxation and Efiling at teachoo.com .
Jail