# Thread: help needed half-life logrithms

1. ## help needed half-life logrithms

the half life of sodium-24 is 14.9h. suppose a hospital buys a 40mg sample of sodium-24.
a.) how much of the sample will remain after 48h?
b.) how long will it be until only 1mg remains?

2. First solve for $A$ .

$Q = Q_0 \times A^t$ where $t$ is in hours. So we have

$20 = 40 \times A^{14.9}$

3. how i do it if i were to put in logs into that equation and put it in my calculator?

4. You do need to use logs here.

$20 = 40 \times A^{14.9}$

$\frac{1}{2} = \times A^{14.9}$

From here apply

$a= b^c \implies c=\log_ba$