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**1. Homework Statement**

Measurements of a certain isotope tell you that the decay rate decreases from 8337 decays/minute to 3174 decays/minute over a period of 5.00 days.

**2. Homework Equations**

R=Ro.e^-lamda/t

then T1/2 = ln(2)/lamda

**3. The Attempt at a Solution**

I converted all the units..

t = 5 days = 432000 seconds

R = 8337 decays/minute = 52.9 decays/s

Ro=3174 decays/minute = 138.95 decays/s

I did:

R=Ro.e^-lamda/t

52.9=138.95 . e^-lamda*432000

lamda = -1.86*10^-6

I am confused.. the lamda should not be a negative number right?

because half-life should be a positive number..

please help me..

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