To model half-life, use the formula [tex]A(t)=A_0 (\dfrac{1}{2})^{ \frac{t}{t_{1/2}} [/tex]. Here, [tex]A(t)[/tex] is the amount remaining after a length of time [tex]t[/tex]. [tex]A_0[/tex] is the amount that you start with. [tex]t_{1/2}[/tex] is the half-life. You plug in 50 for [tex]t_{1/2}[/tex], 10 for [tex]A_0[/tex], and 25 for [tex]t[/tex]. You get [tex]A(t)=10( \frac{1}{2})^{25/50} = 10( \frac{1}{2})^{1/2} = 7.07 \ grams[/tex].
