I think there should be 'greater than or equal' because your statements cannot catch avg values such as 75, 60, 50, and 40.
Also, you should distinct 'greater than' condition and 'less than' condition. For example, use '60 <= avg && avg < 75', not '60<avg<75' (You even switched the orders in your question!).
Finally, if you want to print only one sentence different by average's range, you should use 'else if' to distinguish score ranges.
So the revised version should be...
printf("enter number of 5 subjects");
if (avg >= 75) printf ("Distinction");
else if (60 <= avg && avg < 75) printf("1st Division");
else if (50 <= avg && avg < 60) printf("2nd divison");
else if (40 <= avg && avg < 50) printf("3rd Divison");
else printf("fail"); // You can leave out the 'else if' statement because the last condition (avg < 40) is the only left else condition. (Sorry my english is bad :D)