Explanation:
We're told from the question that 200 students took part in the exercise, so if the total number of girls is 100 then the total number of boys will be;
[tex]\text{Total number of boys =}200-100=100[/tex][tex]\text{Total number of boys that chose Biology}=100-44-37=19[/tex][tex]\text{Total number of boys and girls that chose Biology}=40+19=59[/tex][tex]\text{Total number of boys and girls that chose Chemistry}=39+44=83[/tex][tex]\text{Total number of boys and girls that chose Physics}=21+37=58[/tex][tex]\text{Total of the total row}=59+83+58=200[/tex]To find how many more girls than boys chose Biology, we'll have;
[tex]40-19=21[/tex]So 21 more girls than boys chose Biology.