The isotope 
has a half-life of 7.5 seconds. If a sample contains 144 atoms of 
approximately how many such atoms were there present 30 seconds earlier?
Definitions:
Linear Model
A linear model is a mathematical model that approximates the relationship between a dependent variable and one or more independent variables using a linear equation.
Scatterplot
A statistical graph type that illustrates the association between two variables by displaying data values for a dataset.
Regression Analysis
A technique in statistics for investigating how a dependent variable is related to one or more independent variables.
Slope
The measure of steepness or incline, often represented as a ratio between rise over run in a linear equation.
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