SOLUTION: The first 24 terms of an arithmetic series are 35+42+49...+196.Calculate the sum of ALL natural numbers from 35 to 196 that are not divisible by 7

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Question 1142934: The first 24 terms of an arithmetic series are 35+42+49...+196.Calculate the sum of ALL natural numbers from 35 to 196 that are not divisible by 7
Answer by math_helper(2461) About Me  (Show Source):
You can put this solution on YOUR website!
You can solve this by computing the sum of ALL numbers from 35 to 196, and then subtracting the sum of 35+42+...+196 (because those are all the numbers divisible by 7 in the given range, you will be left with the sum of numbers NOT divisible by 7):

(sum1) 35+36+ ... + 196 = (196+35)*(196-35+1)/2 = 18711


(sum2) 35+42 + ... + 189 + 196 = 7(5+6+...+27+28) = 7(28+5)*(28-5+1)/2 = 2772



(sum1) - (sum2) = 18711-2772 = +highlight%28+15939+%29+