Lara ate $\frac{1}{4}$ of a pie and Ryan ate $\frac{3}{10}$ of the same pie. The next day Cassie ate $\frac{2}{3}$ of the pie that was left. What fraction of the original pie was not eaten?
(A) $\frac{9}{10}$
(B) $\frac{3}{10}$
(C) $\frac{7}{60}$
(D) $\frac{3}{20}$
(E) $\frac{1}{20}$
Together, Lara and Ryan ate $\frac{1}{4}+\frac{3}{10}=\frac{5}{20}+\frac{6}{20}=\frac{11}{20}$ of the pie.

Therefore, $1-\frac{11}{20}=\frac{9}{20}$ of the pie remained.

The next day, Cassie ate $\frac{2}{3}$ of the pie that remained.

This implies that $1-\frac{2}{3}=\frac{1}{3}$ of the pie that was remaining was left after Cassie finished eating. Thus, $\frac{1}{3}$ of $\frac{9}{20}$, or $\frac{3}{20}$ of the original pie was not eaten.

ANSWER: (D)