Final answer:
The correct expression of 31 billion in scientific notation is 3.1 × 10¹⁰. This is done by moving the decimal point left 10 places, resulting in a coefficient between 1 and 10 followed by × 10 raised to the power of the number of places moved.
Step-by-step explanation:
To express the number 31 billion in scientific notation, we have to rewrite it in a form where the number is between 1 and 10 multiplied by a power of 10. The number 31 billion is written as 31,000,000,000 in standard form. To convert it into scientific notation, we need to move the decimal point to the left until we get a number between 1 and 10:
31,000,000,000 = 3.1 billion when the decimal is moved 1 place to the left. Since we originally moved the decimal place 10 places to the left, the exponent for 10 will be 10, resulting in the scientific notation: 3.1 × 10¹⁰.
Therefore, the correct expression of 31 billion in scientific notation is 3.1 × 10¹⁰ (Option A).