Question

Attached.

Answer 1

I am cool with part a.

Answer 2

well even that is gud :)

Answer 3

or If I reframe ur question u want to ask the sol. to part b

Answer 4

yes

Answer 5

u know the formula for sum of an AP
Now put there the first term = 9th term and final term = 20th term and u will get ur answer

Answer 6

\[2\sum_{i=1}^{20}i-2\sum_{i=1}^{8}\]

Answer 7

even that will work........ ,