1. **State the problem:** Add the two numbers expressed in scientific notation: $2.33 \times 10^8$ and $9.87 \times 10^8$. 2. **Formula and rules:** When adding numbers in scientific notation with the same exponent, add the coefficients and keep the exponent the same. 3. **Intermediate work:** $$2.33 \times 10^8 + 9.87 \times 10^8 = (2.33 + 9.87) \times 10^8$$ $$= 12.20 \times 10^8$$ 4. **Simplify the result:** Rewrite $12.20 \times 10^8$ as $1.22 \times 10^9$ by moving the decimal point one place to the left and increasing the exponent by 1. 5. **Final answer:** $$\boxed{1.22 \times 10^9}$$ This is the sum of the two numbers in proper scientific notation.