Namibia normally imports about 50% of its cereal requirements; in drought years food shortages are a major problem in rural areas.
An unemployment rate of at least 50% continues to be a major problem.
An unemployment rate of 50% continues to be a major problem.
An unemployment rate of 40% to 50% continues to be a major problem.
The above list will hopefully provide you with a few useful examples demonstrating the appropriate usage of "major problem" in a variety of sentences. We hope that you will now be able to make sentences using this group of words.