The initial number (2 x 10^4) is in scientific notation. Scientific notation must be written as: a X 10^n, where 0<a<10 and n is an integer. In this case, the number in scientific notation is being raised to the power of 5. When we raise a power by another power, we must multiply the power of all the terms by the additional power. In this case, we would get 2^5 x 10^20, this would be 10 x 10^20. Since the value of 'a' needs to be greater than 0 and less than 10, we need to move the decimal to the left and add another power to our 10: 1 x 10^21.
