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Complete the following activity to find the sum of natural number between 1 and 140. Which are divisible by 4 |
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Answer» ong>Answer: These numbers from an A.P. with a = 4, d = 4 Let, 140 be the nth TERM of A.P. ∴ tn = 140 tn = a + (n – 1) d ∴ 140 = 4 + (n – 1) 4 ∴ 140 = 4 + 4n – 4 ∴ 140 = 4n ∴ n = 140/4 ∴ n = 35 ∴ 140 is 35 term of A.P. Now, We have to find sum of 35 terms i.e. S35, Sn = n/2[2a + (n – 1)d] ∴ S35 = 35/2 [2 (4) + (35 – 1) 4] ∴ S35 = 35/2[8 + 34 (4)] ∴ S35 = 35/2 [8 + 136) ∴ S35 = 35/2 [144] ∴ S35 = 2520 |
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