In a college, The average weight of male students is 50kg and the average weight of female students is 40kg. If the average weight of all students (both male and female) is 47kg and the number of female students in the college is 30, then What is the number of male students in the college?
80
75
20
50
70
Solution
Average weight of male students = 50kg
Average weight of female students = 40kg
Average weight of total students = 47kg
Let the number of students be x, then
$\frac{\left( x-30 \right)\times 50+40~\times 30}{x}=47$
$47x=50x-1500+1200$
$3x=300$
$x=100$
Number of male students $= x - 30 = 100 - 30 = 70$