In this exercise the effort does not have any relation with the code: it is a normally ordered BCD 8 4 2 1 , otherwise with what you seen since the numbers appear blurry: there are errors. Some of the small bars (segments) with which the numbers are drawn are exchanged. Which ones in each file?

For example, the files cod_ag and cod_bc, available in Moodle. When you download the file cod_ag and input the combination 0111, you will see the following.

Hint: This that you see, is a number, isn't it? Which should have been (7)? Check with another combination to find out what can be seen and what should be seen.