At jefferson school, both 6th grade & 7th grade classes take a math test. the average score for the 6th grade is 80 and for the 7th grade is 90. if there are twice as many students, in the 7th grade as there is in the 6th grade, what is the average test score for both grades together?
80+90+90/3 = 86.6. i have to put 86.6 as a fraction in simplest form but i don't know what it is. help please?