An algebra problem by Ritam Podder

S=n(n+1)/2,use this formula to do the sum,where n is number of natural numbers. (200000*200001)/2 =20000100000

We can use the formula for the sum of no.s in the Arithmetic Progression.

S = n(n+1) / 2; hence, we can see here n=200000 (the last term or the no. of terms) therefore,
S = 200000*200000+1)/2 = 20000100000

$A=1+2+3+\ldots+200000$

$2A=200001+200001+200001+\ldots+200001$ ( there are $200000$ " $200001$ ")

$A=\frac{200001\times200000}{2} =\boxed{20000100000}$