$13$ is what percent of $20$?

Percent $= \dfrac{\text{part}}{\text{whole}} \times 100\%$. $\dfrac{13}{20} = 0.65 = 65\%$. Quick mental math: $\dfrac{13}{20} = \dfrac{65}{100}$ by multiplying numerator and denominator by 5. - Trap A ($13\%$) treats $13$ as a percent already. - Trap B ($26\% = 13 \cdot 2$) doubles the wrong number. - Trap C ($50\%$) is the percent for $10/20$, off by one part.