Determining the absorbance of a solution?

Question

Here is the question...

A student analyzes a green solution in a spectophotometer and sets the baseline reading to 97.4% (using distilled water) at the wavelength 450nm. He then obtains a 47.3% reading for his green solution at this same wavelength. Determine the absorbance of the solution at this wavelength.

***
I think I'm over thinking this, since I tried to use Beer's Law to solve, but we've never gone over Beer's Law in this class.

Answer 1

If the student had set the distilled water solution to 100% transmittance (T%), the problem would have been easy using the equation (where A is the Absorbance at 450 nm):

A = 2 - log T%

The best you can hope for is an approximation calculating the Absorbace at 47.3% and then subtracting the Absorbance at 97.4%. Use log tables or log button on your calculator to get the Absorbances.

You should realize that this student made at least one major mistake (which is the reason that the water blank could not be set to T =100%). The wavelength used (450 nm) is in the range of blue to indigo light. A more appropriate wavelength would have been about 510 nm for a green solution. The other question would be is did the student set the 0%T with an opaque object?