Question

5+8+11........n=10 use formula and solv this question

Answer 1

                                                                                           

The series is in AP, So by using formula,

$Sn=\frac{n}{2} (2a+(n-1)d)$

$Sn=\frac{n}{2} (2 *5+(n-1)3)$

$Sn=\frac{n}{2}(3n+7)$

Hope This Helps