Multiple Choice Questions on Find the sum of the AP 3 6 9 hellip hellip n ........ for NDA Exam Preparation

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Multiple Choice Questions

Find the sum of the AP 3 6 9 hellip hellip n ........

Mathematics (NDA) Arithmetic progression
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    Find the sum of the AP 3,6,9,……,n? 

    3n(n+1)/2 

    Correct Answer

    n(n+1)/2 

    Incorrect Answer

    n(n+1) 

    Incorrect Answer

    (d)(n+1) 

    Incorrect Answer
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    Explanation:

    Here , a =3 , d = 3 

    Thus,   Sn = n/2[2a +(n-1)d] 

    = n/2[2×3 + (n-1)×d] 

    = n/2[6 +3n -3] 

    = n/2(3n +3) 

    Sn = 3n(n +1)/2 

    By: bhavesh kumar singh
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