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Ex 5.3, 2 - Find sums (i) 7 + 10 1/2 + 14 + ... + 84 - Ex 5.3

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

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Ex 5.3, 2 Find the sums given below (i) 7 + 101/2 + 14 + ………… + 84 7 + 10 1/2+14+…84 Here, a = 7 d = 10 1/2−7 = 21/2−7 = (21 − 14)/2 = 7/2 Also, last term = 𝒍 = 84 To find sum, first we need to find n Using formula an = a + (n − 1)d Putting a = 7, d = 7/2, an = 84 in the formula 84 = 7 + (n − 1) × 𝟕/𝟐 84 − 7 = (n − 1) × 7/2 77 = (n − 1) × 7/2 77 × 2/7 = (n − 1) 22 = n − 1 n = 22 + 1 n = 23 For sum, we use the formula S = 𝒏/𝟐 (𝒂+𝒍) Putting a = 7, n = 23, l = 84 S = 23/2(7+84) S = 23/2×91 S = 2093/2 S = 1046.5

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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.