An expression containing square roots: $\sqrt{144} + \sqrt{0.0324} - \sqrt{6.76}$

Evaluate each root individually: $\sqrt{144}=12$, $\sqrt{0.0324}=0.18$ (since $18^2=324$), and $\sqrt{6.76}=2.6$ (since $26^2=676$). Then simply perform addition and subtraction.

Confusing the number of decimal places when taking the square root; for example, $\sqrt{0.0324}$ must have two decimal places because $0.18 \times 0.18 = 0.0324$.

This concept is fundamental for simplifying complex expressions in Algebra and Mensuration problems involving geometry.