$24.424 + 5.656 + 1.131 + 0.089 = $ $x$

### Concept & Strategy This is an exercise in precise decimal addition, emphasizing careful handling of carry-overs across the decimal point to reach a simplified final number. ### Step-by-Step Solution * Align the numbers vertically according to their decimal points: * $24.424$ * $05.656$ * $01.131$ * $00.089$ * Sum the thousandths column: * $4 + 6 + 1 + 9 = 20$ (Write $0$, carry over $2$) * Sum the hundredths column: * $2 + 5 + 3 + 8 + 2 \text{ (carry)} = 20$ (Write $0$, carry over $2$) * Sum the tenths column: * $4 + 6 + 1 + 0 + 2 \text{ (carry)} = 13$ (Write $3$, carry over $1$) * Sum the units column: * $4 + 5 + 1 + 0 + 1 \text{ (carry)} = 11$ (Write $1$, carry over $1$) * Sum the tens column: * $2 + 1 \text{ (carry)} = 3$ * The raw sum is $31.300$. Trailing zeros after a decimal point hold no value, simplifying the answer to $31.3$. ### Exam Strategy & Shortcut **Partial Addition:** Focus on the decimal portion first. $0.424 + 0.656 + 0.131 + 0.089$ Notice that $0.424 + 0.656 = 1.080$. And $0.131 + 0.089 = 0.220$. Add them together: $1.080 + 0.220 = 1.300$. Now add the whole numbers: $24 + 5 + 1 + 0 = 30$. Total: $30 + 1.3 = 31.3$. This mental grouping is often faster and less error-prone than strict vertical addition. ### Common Pitfall Failing to drop trailing zeros correctly, leading to confusion between $31.300$ and options like $31.003$ or $31.03$. Aligning the decimal places improperly is also a common error for those rushing. ### Final Answer **Therefore, the correct answer is $31.3$.**