a. find the sum of the first 200 pos. intergers of

1 + 2 + 3 + 4 + . . . + 200

is it

Tn =a+(n-1)d

200=1+(n-1)1

=1+n-1

200=n

n=200

then

Sn=n/2(a+l)

S200=200/2(1+200)

=100 X 201

=20100

is that right?

b. series 1 + 5 + 7 + 11 + . . . + 199 is formed by omitting all those which are multiples of 2 or 3 up to the first 200 intergers. Find the sum

how do you do this??