A Radioactive Sample Has a Half-Life Of $10 \mathrm {~min}$ What Fraction of the Sample Is Left After

A radioactive sample has a half-life of $10 \mathrm {~min}$ . What fraction of the sample is left after $40 \mathrm {~min}$ ?

A) $1 / 4$
B) $1 / 16$
C) $1 / 8$
D) $1 / 2$