You can deduct on Schedule A (Form 1040) only the amount of your medical and dental expenses that is more than 7.5% of your AGI(Form 1040, line 38).
In this publication, the term "7.5% limit" is used to refer to 7.5% of your AGI. The phrase "subject to the 7.5% limit" is also used. This phrase means that you must subtract 7.5% (.075) of your AGI from your medical expenses to figure your medical expense deduction. taxmap/pubs/p502-002.htm#en_us_publink1000178857
Your AGI is $40,000, 7.5% of which is $3,000. You paid medical expenses of $2,500. You cannot deduct any of your medical expenses because they are not more than 7.5% of your AGI.