Genetics- Question about map units?

Well since map units are believed to be proportional to the percent of recombination you can say that the % for recombination is 25% but it's hard to say for the %population. To be able to calculate the map units, you need the number in the population of the parental genotypes (non-crossing over the most abundant in the population), the single cross overs, and the double cross overs. I really don't know the answer (we just took this up in cl the other week). Your question is the reverse of the usual method and we weren't taught this yet. Hope this helps.