HalfLifes
posted by Sarah .
How much of a 6gram sample of silver105m would remain after 4 minutes?
Half life=7.2 minutes

k = 0.693/t_{1/2}
Substitute k into the equation below.
ln(No/N) = kt.
No = 6
N = unknown
k = from above
t = 7.2 min
I get approximately 4 g remaining. 
Great! But, so that I can understand it in the future, can you tell me what the value of k is a little more clearly? how do you do a subscript of 1/2?

The half life is given in the problem (last line you typed) of 7.2 minutes.
I write a t_{1/2}
To turn on subscript type < followed by sub followed by >. Then type the 1/2. To turn subscript off type < followed by /sub followed by >