Solution:
k1 = 0.1d-1
k2 = 0.005 d-1
k3 = 0.02 d-1
t = 7 days
The integrated activity = 0.04*[0.1e(-0.1*7) + 0.3e(-0.05*7) + 0.6e(-0.02*7)]
= 0.04*[0.04966 + 0.21141 + 0.5216]
= 0.0313068