Need help with formula so results appear a certain way

i have this formula, but it doesn't seem to work.  Can anybody please tell me why?  I want all companies with specific Gross Annual Revenue to show a range in the results instead of the GAR that was inputted.

Case when To_NUMBER ({customer.custentity_grossannualrevenue}) >0 and TO_NUMBER ({customer.custentity_grossannualrevenue}) = <10 then 'Under $10 million'
when ({customer.custentity_grossannualrevenue}) = > 10 and <25 then ‘$10-24 million’
when ({customer.custentity_grossannualrevenue}) = >24 and <50 then ‘$25-49 million’
when ({customer.custentity_grossannualrevenue}) = >49 and <100 then ‘$50-99 million’
when ({customer.custentity_grossannualrevenue}) = >99 and <250 then ‘$100-249 million’
when ({customer.custentity_grossannualrevenue}) = >249 and <500 then ‘$250-499 million’