Question 427020
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Hi
Let x and (1-x) represent the fractional portion of teachers and students respectively 
 35x + 15(1-x) = 20
        20x = 5
          x = 1/4, are teachers and 3/4 are students.
ratio of teachers to students is 1:3

CHECKING our Answer***
 .25*35 + .75*15 = 8.75 + 11.25 = 20