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NDA 2020 Maths · Mathematics · Sequences and Series · medium

The sum of all the multiples of 7 lying between 100 and 500 is

Single correct option

The sum of all the multiples of 7 lying between 100 and 500 is
  1. A. 17759
  2. B. 17150
  3. C. 17157
  4. D. 16555
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Answer: (C) 17157

The multiples form an AP from 105105 to 497497 with d=7d=7. The number of terms is 497−1057+1=57\dfrac{497-105}{7}+1=57. The sum is 572(105+497)=57×301=17157\dfrac{57}{2}(105+497)=57\times301=17157. Counting 56 terms is the usual slip.
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Original question written in the NDA 2020 Maths pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake