Question 461892
Let b = # of boys in the school that took the exam, 
g = of girls in the school that took the exam.
==> The number of students that took the exam is b + g.
Then the sum of all the scores for the boys that took the exam is 71b, while the sum of all the scores for the girls that took the exam is 73g.

==> 71b + 73g is the sum of all scores of the students that took the exam.
By the given, {{{(71b + 73g)/(b + g) = 71.8}}},
or {{{71b + 73g = 71.8b + 71.8g}}}, or {{{1.2g = 0.8b}}}, or {{{b/g = 1.2/0.8 = 1.5}}}.