A Radioactive Substance Containing $4.0 \times 10 ^ { 16 }$

Short Answer

A radioactive substance containing $4.0 \times 10 ^ { 16 }$ unstable atoms has a half-life of $2.0$ days. What is its activity (in curies, Ci) after $1.0$ day? ( $\mathrm { Ci } = 3.70 \times 10 ^ { 10 } \mathrm {~Bq}$ )