Question: Subtract. Write your answer in scientific notation.
$8.4\times 10^{9} - 5.2\times 10^{8}$
1. **State the problem:** We need to subtract $8.4\times 10^{9}$ and $5.2\times 10^{8}$ and write the answer in scientific notation.
2. **Recall the rule:** To subtract numbers in scientific notation, they must have the same power of 10.
3. **Rewrite the terms with the same exponent:**
$$8.4\times 10^{9} = 84\times 10^{8}$$
4. **Perform the subtraction:**
$$84\times 10^{8} - 5.2\times 10^{8} = (84 - 5.2) \times 10^{8} = 78.8 \times 10^{8}$$
5. **Convert to proper scientific notation:**
$$78.8 \times 10^{8} = 7.88 \times 10^{9}$$
6. **Final answer:**
$$7.88 \times 10^{9}$$