The fraction of medium sized shirt is
.
Step-by-step explanation:
Given,
of the shirts are small sized.
of the shirts are large sized.
To find the fraction of medium sized.
Let us take total number of shirt = 1
Number of small sized shirt =c
Number of large sized shirt = 
So,
Total number of large and small sized shirt = 
= 
Hence,
Number of medium sized shirt = 
= 