40. We note that 2.42 min = 145.2 s. We are asked to plot (with SI units understood)



ln R =ln R0e-t + R0e- t

where R0 =3.1 × 105, R0 =4.1 × 106,  =ln 2/145.2 and  =ln 2/24.6. Our plot is shown below.
15
14
13
12
11
10
0 100 200 300 400 500 600
t
110
We note that the magnitude of the slope for small t is  (the disintegration constant for Ag), and
108
for large t is  (the disintegration constant for Ag).