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      Question

      Find the sum of all natural numbers less than 500 which

      are divisible by 7.
      A 12,457 Correct Answer Incorrect Answer
      B 17,892 Correct Answer Incorrect Answer
      C 19,802 Correct Answer Incorrect Answer
      D 11,092 Correct Answer Incorrect Answer

      Solution

      Smallest multiple of 7: 7 Largest multiple of 7 less than 500: 7 Γ— 71 = 497 So series: 7, 14, ..., 497 is an AP with a = 7, d = 7, last term l = 497 Number of terms n: l = a + (nβˆ’1)d β‡’ 497 = 7 + (nβˆ’1)7 497 βˆ’ 7 = 7(n βˆ’ 1) β‡’ 490 = 7(n βˆ’ 1) n βˆ’ 1 = 70 β‡’ n = 71 Sum = n/2 Γ— (first + last) = 71/2 Γ— (7 + 497) = 71/2 Γ— 504 = 71 Γ— 252 = 17,892.

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