If 1+2+3+...+n=n (n+1), then
2 (1+3+5+....+89)=?
Options: A) 4100 B) 4050 C) 4250 D) 4350 E) 4450
Explanation :   To solve this use the formula of AP,   Sn= (n/2)(a+l) ................(1)   To find n, use   =&gt; Tn= a+(n-1)d   =&gt; 89=1+(n-1)2   =&gt; n=45   Use value of n in (1)   then,   Sn = (45/2)(1+89) = 2025   Ans:- 2(Sn) = 4050   Answer : 4050
<result>B</result>
If 1+2+3+...+n=n (n+1), then
2 (1+3+5+....+89)=?