Get it wrong in the first attempt!

The question if better formatted looks like: $1 + 2 + 3 + \ldots + 999 + 1000 + 1001 \times 0$ . Note that 0 is multiplied only by 1001. Thus we get:

$1 + 2 + 3 + \ldots + 999 + 1000$

Using sum of natural numbers we get:

$1 + 2 + 3 + \ldots + 999 + 1000 = \dfrac{1000 \times 1001}{2} = \boxed{500500}$

Apply first the "Order of Operations"

$1+2+3+...+999+1000+1001\times 0 = 1+2+3+...+999+1000+0= 1+2+3+...+999+1000$

The sum of the first $n$ natural numbers is given by the equation

$S = \dfrac{n}{2}(n+1)$

Substitute:

$S = \dfrac{1000}{2}(1000+1)=500(1001)=\color{#3D99F6}\large{\boxed{500500}}$ $\color{#69047E}\boxed{\text{answer}}$

It can be written as $1 + 2 + 3 + \ldots + 999 + 1000 = \frac{1000 \times 1001}{2} = \color{#3D99F6}{\boxed{500500}}$

According to BODMAS rule, we must solve multiplication before addition.So, the problem becomes

1+2+3+......1000+0

This is the sum of first 1000 natural numbers.So, our answer is 500500