direct and inverse equuation

Question

the absorbance varies directly with the concentration of an unknown substance, and the absorbance is 0.3 when the concentration is 100mg/dL. find the absorbance when the concentration is 300mg/dL

Answer 1

With direct variation, an increase in concentration leads to an increase in absorbance.  We can assume that the curve passes through (0,0), where a concentration of zero leads to zero absorbance.  Therefore there is a positive linear relationship.  If the concentration is tripled, the absorbance will also triple.

Allow A=abs.

Allow x = conc. in mg/dL

Allow m = slope

 if A = 0.3 and x=100;

0.3 = 100*m

m = 0.3/100 = 0.003.

A = 0.003x

Solve for x = 300

A = 0.003*(300) = 0.9