A property and casualty insurance company categorizes its policyholders into three groups: low risk, medium risk, or high risk. 25% of the policyholders are low risk and 30% are high risk. The high risk policyholders are three times as likely as medium risk policyholders to file an insurance claim and the medium risk policyholders are twice as likely as the low risk policyholders to file an insurance claim. Determine the proportion of the insurance claims filed by medium risk policyholders.