Question 328054
In a science test a class of 30 students had an average of 80.
 The 20 girls had an average of 85.
 What's the average of the 10 remaining boys?
:
Let x = av of the 10 boys
:
{{{(20(85)+10x)/30}}} = 80
multiply both sides by 30, results
20(85) + 10x = 30(80)
1700 + 10x = 2400
10x = 2400 - 1700
10x = 700
x = {{{700/10}}}
x = 70 is the av of the 10 boys