IDNLearn.com offers a unique blend of expert answers and community-driven knowledge. Join our Q&A platform to receive prompt and accurate responses from knowledgeable professionals in various fields.

A 221.3 ng sample of an unknown radioactive substance was placed in storage and its mass measured periodically. After 47 days the amount of radioactive substance had decreased to 27.66 ng. How many half‑lives of the unknown radioactive substance have occurred?