(12% of 555) + (15% of 666) = $x$

### Concept & Strategy This problem demands basic percentage calculations. The most efficient strategy is to split the percentages into manageable chunks (like $10\% + 2\%$ or $10\% + 5\%$) to perform the math mentally, rather than writing out fraction multiplications. ### Step-by-Step Solution * **Given**: $(12\% \text{ of } 555) + (15\% \text{ of } 666) = x$ * **Calculation**: 1. Solve the first bracket: $12\% \text{ of } 555$ Break $12\%$ into $10\% + 2\%$. $10\% \text{ of } 555 = 55.5$ $1\% \text{ of } 555 = 5.55$, so $2\% = 5.55 \times 2 = 11.1$ Total for first bracket $= 55.5 + 11.1 = 66.6$ 2. Solve the second bracket: $15\% \text{ of } 666$ Break $15\%$ into $10\% + 5\%$. $10\% \text{ of } 666 = 66.6$ $5\%$ is half of $10\%$, so half of $66.6 = 33.3$ Total for second bracket $= 66.6 + 33.3 = 99.9$ 3. Add the two results together: $$x = 66.6 + 99.9$$ $$x = 166.5$$ ### Exam Strategy & Shortcut Look for patterns! Notice that $15\% \text{ of } 666$ is the same as $10\% (66.6) + 5\% (33.3) = 99.9$. For $12\% \text{ of } 555$, you can multiply $12 \times 5 = 60$, $12 \times 5 = 60$, $12 \times 5 = 60$. Shifting decimals gives $60 + 6 + 0.6 = 66.6$. Adding $66.6 + 99.9$ is easiest if you treat $99.9$ as $(100 - 0.1)$. $66.6 + 100 = 166.6$. Subtract $0.1$ to get $166.5$. ### Common Pitfall Converting everything to exact fractions like $\frac{12}{100} \times 555$ and doing long multiplication ($12 \times 555$) is a massive time drain and increases the risk of carrying errors during addition. Always use decimal shifting for $10\%$, $5\%$, and $1\%$ values. ### Final Answer **Therefore, the correct answer is 166.5.**