Question

the ratio of the number of girls to the number of boys in my a classroom , was 5:4. When 10 remained girls left the classroom ,the ratio of the number boys of  to the number of girls became 4:3 . How many students were in the classroom at first ?

Answer 1

because the ratio of the number of girls to the number of boys in my a classroom , was 5:4 => the ratio of the number of boys to the number of student in my classroom was 4 : 9

When 10 remained girls left the classroom ,the ratio of the number boys of  to the number of girls became 4:3 => the ratio of the number of boys to the number of student in my classroom ( after 10 remained girls left) was 4 : 7 

=> the number of student in my classroom at first were 10 : ( 9 - 7 ) x 9 = 45 ( students )

                  so the answer is 45 students