In scientific notation, how do you express 5×10^7 divided by 2×10^−9?

To solve the problem of dividing 5×10^7 by 2×10^−9 in scientific notation, we start by applying the rules of division for numbers in scientific notation.

When dividing two numbers in scientific notation, you can divide their coefficients and then subtract the exponents. In this case, you need to divide the coefficients (5 divided by 2) and handle the powers of ten by subtracting the exponent of the denominator from the exponent of the numerator.

The calculation goes as follows:

1. Take the coefficients: 5 divided by 2 gives you 2.5.
2. For the exponents, you have 10^(7 - (-9)). This simplifies to 10^(7 + 9), which equals 10^16.

Thus, the result of the division would be 2.5 multiplied by 10^16, expressed as 2.5×10^16.

From the choices given, it's evident that the reasoning aligns with option D (2.5×10^18) due to a miscalculation in handling the exponents in option B. Therefore, 2.5×10^16 is the correctly simplified form of the division.