Study the given pie - chart and table carefully and answer the question that follows. The percentage wise distribution of lecturers in five different subjects in a university is shown in the pie chart.

The total number of lecturers is 500.

Ratio of male to female lecturers:

Lecturers	Males : Females
Mathematics	7 : 3
Physics	2 : 3
Chemistry	4 : 1
Botany	3 : 5
Zoology	2 : 5

What is the difference in the number of female lecturers in chemistry and Mathematics?