A number, when increased by 100%, gives 2820. The number is:

The correct answer is 1410.

Step 1: Define the variable and understand the problem
Let the unknown original number be represented by $x$.

Increasing a number by 100% means adding 100% of the number to itself.

Step 2: Express 100% as a decimal or fraction
100% of $x$ is equal to:
$100\%\times x=\frac{100}{100}\times x=1\times x=x$

Step 3: Set up the equation
When the original number $x$ is increased by 100% of itself, the result is 2820:
$x+x=2820$

Step 4: Solve for $x$
Combine like terms:
$2x=2820$

Divide both sides by 2:
$x=\frac{2820}{2}$

$x=1410$

Therefore, the original number is 1410.