Question

Find sum of the following series 0.7+0.71+0.72+_ _ _ _ _ _ _ _ to n terms

Answer 1

Here.

a=0.7
d=0.71-0.7=0.01

so Sum upto n Terms=
$\frac{n}{2} (2(0.7) + (n - 1)0.01) \\ = \frac{(n \times 2 \times 0.7) \: + 0.01n(n - 1)}{2} \\ = 0.7n + ( \frac{0.01 {n}^{2} - 0.01n) }{2} \\ = 0.7n + 0.005 {n}^{2} - 0.005n \\ = 0.005 {n}^{2} + 0.7n - 0.005n \\ = 0.005 {n}^{2} + 0.695n \\ = \frac{5 {n}^{2} + 695n }{1000}$
Hope it Helps...
Regards,
Leukonov.