1. Calculate the sum: $(2.4 \times 10^6) + (5.3 \times 10^6)$. Express your answer in scientific notation: ___.
2. What is the sum of $(1.5 \times 10^9)$ and $(7.2 \times 10^9)$?
3. Find the sum of $(4.5 \times 10^{-4})$ and $(2.1 \times 10^{-4})$. The sum is ___ $\times 10^{-4}$.
4. Which expression is equivalent to $(5.2 \times 10^8) + (1.6 \times 10^8)$ by the distributive property?
5. Calculate the sum: $(3.7 \times 10^{-5}) + (5.2 \times 10^{-5}) = \text{\_\_\_}$.
6. Calculate the following expression and write the answer in scientific notation: $(8.9 \times 10^5) - (4.7 \times 10^5) = \_\_\_$
7. Find the difference: $(5.6 \times 10^{-4}) - (1.3 \times 10^{-4})$. The result is ___.
8. What is the result of $(3.5 \times 10^8) - (9.2 \times 10^8)$?
9. Subtract the numbers and express the result in scientific notation: $(9.85 \times 10^6) - (2.15 \times 10^6) = \_\_\_$
10. When subtracting two numbers in scientific notation, $(a \times 10^n) - (b \times 10^n)$, which part of the expression remains unchanged in the result?