Question:

What is the sum of all natural numbers strictly between 100 and 1000 which are multiples of 5?

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For AP sums, always prefer: \[ S=\frac{n}{2}(a+l) \] when first and last terms are easily identifiable.
Updated On: Jun 12, 2026
  • \(97,450\)
  • \(98,450\)
  • \(98,550\)
  • \(97,650\)
Show Solution
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The Correct Option is B

Solution and Explanation


Step 1:
Identify the AP. Multiples of 5 between 100 and 1000: First term: \[ 105 \] Last term: \[ 995 \] Common difference: \[ d=5 \]

Step 2:
Find number of terms. \[ n=\frac{995-105}{5}+1 \] \[ =\frac{890}{5}+1 \] \[ =178+1=179 \]

Step 3:
Use sum formula. \[ S_n=\frac{n}{2}(a+l) \] \[ S=\frac{179}{2}(105+995) \] \[ =\frac{179}{2}(1100) \] \[ =179\times 550 \] \[ =98450 \] \[ \boxed{98,450} \]
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