Correct Response: B. The sum of two numbers expressed in scientific notation, where both expressions are in terms of the same power of 10 (exponent), can be found by adding the first parts (coefficients), and keeping the exponent the same. This can be shown arithmetically as follows: (3.5 ´ 103) + (3.5 ´ 103) = (3.5 + 3.5) ´ (103) = (7) ´ (1000) = 7,000. Answer choice A is the average of two numbers. Answer choice C is found by leaving the coefficients of the numbers unchanged, and adding the exponents. Answer choice D comes from adding the coefficients of the numbers, and adding the exponents.
