Acollector has 120 movie posters and 100 band posters. she wants to sell 24 movie posters but still have her poster collection maintain the same ratio of 120: 100. if she sells 24 movie posters, how many band posters should she sell? explain

Yes, the ratio      120 movie posters
                            must be maintained.  To use this info,
                            100 band posters   write an equation of ratios as follows:

120 movie posters         100 band posters
=  
   24 movie posters                        x

Then 120x=2400, or x = 20.

Is the ratio 20/24 the same as the ratio 100/120?  It MUST be.