Answer
$300,000,000$
Work Step by Step
We are given that the estimated world population in 1 C.E. was $3.0\times10^{8}$. Since the exponent is positive, move the decimal 8 places to the right.
Note that 8 places to the right will be 8 decimal places past the last digit (3), so we will add 8 zeroes after 3.
$3.0\times10^{8}=300,000,000$
