18.

Simplify the expression. Write the answer using scientific notation.

Astronomers measure large distances in light-years. One light-year is the distance that light can travel in one year, or approximately 5,880,000,000,000 miles. Suppose a star is 13.6 light-years from Earth. In scientific notation, how many miles away is it?

7.9968 x 1013 miles

5.88 x 1012 miles

1.36 x 1012 miles

5.88 x 1013 miles

1 answer

To determine the distance from Earth to the star in miles using scientific notation, we should multiply the distance in light-years by the distance light travels in one light-year.

Given:
- One light-year ≈ 5,880,000,000,000 miles
- Distance to the star = 13.6 light-years

First, write the distance of one light-year in scientific notation:
\[ 5,880,000,000,000 \text{ miles} = 5.88 \times 10^{12} \text{ miles} \]

Next, multiply the distance in light-years by the distance one light-year in scientific notation:
\[ 13.6 \times (5.88 \times 10^{12}) \]

We'll perform the calculation in two steps:
1. Multiply the base numbers:
\[ 13.6 \times 5.88 = 79.968 \]

2. Apply the rules of exponents (add the exponents when multiplying):
\[ 79.968 \times 10^{12} \]

Finally, convert the result to proper scientific notation:
\[ 79.968 \times 10^{12} = 7.9968 \times 10^{13} \]

So, in scientific notation, the star is:
\[ 7.9968 \times 10^{13} \text{ miles away from Earth} \]

Therefore, the correct answer is:
\[ 7.9968 \times 10^{13} \text{ miles} \]

This matches the first option in the provided choices.