Question= Find the sum of all the odd numbers up to and including 99,999.

Question

Would a=1 because its the first odd number in the sequence? And would d=2 ?

So then would you do S99,999= 49999.5(2+99,998(2))
Then divide by two?

Answer 1

yes, a=1,d=2 but there are 50000 terms, so

S = 50000/2 (2+49999(2))

or, since you know the first and last term,

S = 50000/2 (1+99999)

there are 50,000 odd numbers
The sum of the first n odd numbers is n^2.

Answer 2

Thank you !