There are 10 boys and 20 girls in a class. The class has a test. The mean mark for all the class is 60. The mean mark for the girls is 54. Work out the mean mark or the boys.

Total mark for whole class is 3060= 1800Total mark for girls is 2054= 1080
Therefore subtract smaller from larger to get total mark for boys, and divide that number by 10 to yield 72.