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Q.

What is the sum of first 20 multiples of 13?


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a

2720

b

2730

c

2740

d

2750  

answer is B.

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Detailed Solution

The given multiples of 13 are, 13,26,39,..... The numbers form an AP with first term 13 and common difference 13.
So, we get
a=13,d=13,n=20 We know that sum of first n terms of an AP,
Sn=n2[2a+(n-1)d] On substituting the values, we get
⇒S20=202[2×13+(20-1)13] ⇒S20=10[26+19×13] ⇒S20=10[26+247] ⇒S20=2730 Therefore, the sum of first 20 multiples of 13 is 2730.
Hence, the correct option is 2.
 
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