Answer :
You know that 2/9 of the students of the school are sixth graders.
To determine how many students the said fraction represents, you have to multiply the total number of students by 2/9:
a) The total number of students is 90
Multiply 90 by 2/9 to determine the number of sixth graders.
[tex]90\cdot\frac{2}{9}=20[/tex]→ There are 20 sixth graders in this school.
b) The total number of students is 27
Multiply 27 by 2/9 to determine the number of sixth graders.
[tex]27\cdot\frac{2}{9}=6[/tex]→There are 6 sixth graders in this school.
c) If the total number of students is represented by "x", then the total number of sixth graders will be x multiplied by 2/9:
[tex]\frac{2}{9}x[/tex]d) This time we know that there are 42 sixth graders in the school. To determine to the total number of students you have to divide 42 by 2/9, or, multiply 42 by the reciprocal fraction.
I will multiply the number of sixth-graders by the reciprocal fraction
[tex]42\cdot\frac{9}{2}=189[/tex]→There are 189 students in this school.