A human body requires 0.01 Curie activity of radioactive substance after 24 hours. Half life of radioactive substance is 6 hours. Then max. activity of radioactive substance that can be injected will be : -

The activity at the end of 24 hours must be 0.01 Ci.
Number of half lives in 24 hours: $n = \dfrac{24}{6} = 4$
Activity after n half lives $= \dfrac{A_0}{2^n}$
$\dfrac{A_0}{2^4} = 0.01 \Rightarrow A_0 = 0.01 \times 16 = 0.16$ Ci
So 0.16 Ci must be injected.