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Ex 5.3, 7 - Find the sum of first 22 terms of an AP - Ex 5.3

Ex 5.3, 7 - Chapter 5 Class 10 Arithmetic Progressions - Part 2
Ex 5.3, 7 - Chapter 5 Class 10 Arithmetic Progressions - Part 3

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Ex 5.3, 7 Find the sum of first 22 terms of an AP in which d = 7 and 22nd term is 149. Given 22nd term = a22 = 149 Common difference = d = 7 We know that an = a + (n – 1) d Putting n = 22 , d = 7 , an = 149 149 = a + (22 – 1) × 7 149 = a + 21 × 7 149 = a + 147 149 = a + 147 149 – 147 = a 2 = a a = 2 Now, we need to find sum of first 22 terms And we are given a22 = 149 So, last term = l = 149 We use the formula Sn = 𝒏/𝟐 [ a + l ] Putting a = 2, n = 22, l = 149 = 22/2 [2 + 149] = 11 ×151 = 1661 Hence, Sum of first 22 terms is 1661

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Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 12 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.