# How do you subtract 840000000 - 42000000 and write the answer in scientific notation?

The answer is $7.98 \times {10}^{8}$.
$840 000 000 - 42 000 000 = 798 000 000$
In order to convert $798000000$ to scientific notation, move the decimal to the left eight places so that the coefficient is $7.98$. Since the decimal is moved to the left eight places, the exponent on the base 10 is positive eight. So the number in scientific notation is $7.98 \times {10}^{8}$.