Teachers Notes:
A good Web site for review of nuclear chemistry.

Problem 1:
₂₇Co⁵⁹ + ₀n¹ → ₂₇Co⁶⁰

Problem 2:
₂₇Co⁶⁰ → ₂₈Ni⁶⁰ + _-1e⁰ + ₀γ⁰

Problem 3:
number of half-lifes (n) = 26.4/5.27 = 5.01 half-lives

Amount remaining = (initial amount)(1/2)ⁿ
Amount remaining = (100.0g)(1/2)^5.01=3.10 g remaining