Given the initial weight of 1 mg of radioactive ${ }_{27}^{60} \mathrm{Co}$ (half-life $=5.27$ years), the amount disintegrated in 1 year (rounded off to two decimal places) is ____ mg.
Answer
SELF-PRACTICE — the source book printed no answer.
Nothing is invented here, so this question has no answer on record.
Explanation
Answer: 0.12 mg — Fraction left = e^(−0.693 × 1/5.27) = e^(−0.1315) = 0.877, so 1 − 0.877 = 0.123 mg has decayed.