1/4 of the pupils in a class are girls .4/9 of the boys in the class wear spectacles.what fraction of the pupils in the class are boys who d

1/4 are girls so 3/4 are boys

4/9 of the boys wear glasses so 5/9 of the boys do not wear glasses.

$$\frac{3}{4}\times\frac{5}{9}=\frac{5}{12}$$

so  $$\frac{5}{12}$$   of the students are boys who do not wear glasses.  Just like Alan told you 

Let the number of pupils be n.  There are n/4 girls, hence 3n/4 boys.  

(4/9)*3n/4 = n/3 boys wear spectacles, so 3n/4 - n/3 = 9n/12 - 4n/12 = 5n/12 boys don't.  So the boys who don't wear spectacles, expressed as a fraction of the number of pupils in the class is 5/12.

5/12 of the boys do not wear glasses