Question

1 + 2 + 3 + ... + 19 + 20

Answer 1

Answer:

Let, The A.P be;

A.P.: 1,2,3...20

Here, a=1, d=1, n=20 and l=20

∵ Sn=(n/2)(a+l)

» S₂₀=(20/2)(1+20)

» S₂₀=10(21)=210

∴ S₂₀=210 is the value of 1+2+3+...+19+20.

Answer 2

Answer:

210

Step-by-step explanation:

nx(n+1)/2

n=20

20*21/2

=210