In a class of 36 students ,19 read biology ,16 read chemistry and 5 were not allowed to read both subjects. illustrate the information with a venn diagram

I think you mean 5 were not allowed to read either so you really have 31

b = both
19 - b = only biology
16 - b = only chem
b + 19-b + 16-b = 31
- b + 35 = 31
b = 4 = both
19-4 = 15 only bio
16-b = 12 = only chem
5 do none