Step-by-step explanation:
Given that after [tex]t[/tex] hours,the number of kilograms [tex]y[/tex] of the radio active material is 0.23(0.91)t
[tex]y=0.23(0.91)t[/tex]
rate of decrease of this radio active element=[tex]\frac{dy}{dt}[/tex]
[tex]\frac{dy}{dt}[/tex] represents the slope of the graph [tex]y\text{ vs }t[/tex]
Slope is [tex]\frac{y_{2}-y_{1}}{t_{2}-t_{1}}[/tex],which is the rate at which [tex]y[/tex] decreases with time.
[tex]\frac{dkt}{dt}=k[/tex] for constant k
calculate [tex]y\text{ vs }t[/tex] =[tex]\frac{d(0.23(0.91)t)}{dt} =0.2093[/tex]