Mean score of a class is 70, mean score of boys is 60 and mean score of girls is 75. What's the percentage of girls in the class ???
Suppose there are x girls and y boys in the class
Suppose the sum of the girls' scores is A and the sum of the boy's score is B
Mean score of a class is 70,
That translates as
= 70
or as
mean score of boys is 60
That translates as
= 60
or as
and mean score of girls is 75.
That translates as
= 75
or as
What's the percentage of girls in the class ???
That question translates as
What is "?
What is ?
So we have this system of equations:
and we want to find
We want to eliminate A and B because
doesn't contain them.
Clear them all of fractions:
and we want to find
Substitute 60y for B and 75x for A in the first one:
We want to find
So we substitute 2y for x
So rd of the class are girls.
What percentage is that? %.
Edwin