Whatever value of x you input to the function , the function's value is always 5.
This is seen when you examine the graph of f(x) = 5. It is a straight horizontal line passing through y = 5. For every value of x along the line, f(x) = y = 5.
Usually, when there is contamination the smallest amount can have huge ramifications in the data collected. In this scenario, if in a "clean" environment the trait is found in 2/10 frogs then anything above this number should be considered contaminated. This is because data above this ratio would be considered uncommon or rare and this unique occurrence can be most likely tied to the only new factor which would be the contamination. Therefore the minimum number of frogs with this trait in the sample would be 3.
