Mr Brown gives his class a test. The 15 girls in the class get a mean mark of 75%
The 20 boys in the class get a mean mark of 60%
Nick says that because the mean of 75 and 60 is 67.5 then the mean mark for the whole
class in the test is 67.5%
Nick is not correct.
Is the correct mean mark less than or greater than 67.5%?
You must justify your answer.