Utterly Confused About Nuclear Decay

Nuclear decay problems normally use one or both of the following equations  

The terms Nt and N0 may have many different units. The only restriction on the units is that these two terms have the same units. If they do not have the same units, you will need to convert one of the units. Both t and t1/2 will have units of time. Any time unit may be present. The rate constant (decay constant), k, will have units of time-1. Any time unit maybe present. The time units for t, t1/2, and k must agree. If the units do not agree, you will need to make a conversion. 

Determine the decay constant for iron-55. The half-life of iron-55 is 2.7 years. 

You should begin a problem of this type by recopying and labeling each of the known and unknown variables  

These two variables appear in the equation t1/2 = (In 2)/k. We can rearrange this equation to find k, and enter the value for the half-life  

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