Answer:
3/16
Step-by-step explanation:
Boys with glasses are 1/(1+6) = 1/7 of boys. Boys are 7/(7+5) = 7/12 of the group.
Girls with glasses are 1/(1+3) = 1/4 of girls. Girls are 5/(7+5) = 5/12 of the group.
The fraction of the group that wears glasses is ...
(1/7)(7/12) +(1/4)(5/12) = 1/12 +5/48 = 9/48 = 3/16
3/16 of the students wear glasses.
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Additional comment
It appears we can choose a multiple of 48 students to work out the detailed numbers. For 48 students, the ratio of boys to girls is 28 : 20. The ratio of boys with glasses to those without is 4 : 24, and the similar ratio for girls is 5 : 15. In our group of 48 students, 4 boys and 5 girls = 9 students wear glasses. The fraction is 9/48 = 3/16 as shown above.
