Question

For AP, with a=100, d=50 and n=21, find Sn.​

Answer 1

Step-by-step explanation:

Sn=[2a+(n-1)d]

Sn=[200+20x50]

=200+1000

Sn=1200

Answer 2

Answer:

Sn=n/2{2a+(n-1)d}

=21/2.{2.100+(21-1).50}

=21/2(200+20.50)

=21/2(200+1000)

=21/2×1200

=21×600

=12600