Find the sum of the first 15 multiple of 8

1.	Find the sum of the first 15 multiple of 8
Answer» The positive integers which are multiple of 8 are:8,16,24,................up to 15 termsIt forms an arithmetic series.Now first term a = 8, common difference d = 8, number of terms n = 15Now sum of first 15 terms of AP = (n/2) × {2a + (n-1) × d}= (15/2)× {2× 8 + (15-1)× 8}= (15/2)× (16 + 14× 8)= (15/2) × (16 + 112)= (15 × 128)/2= 15 × 64 (when 64 and 2 is divided by 2) = 960So sum of first 15 terms which are multiple of 8 = 960 960

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