The average marks obtained by the boys and girls in a class are 52 and 42 respectively. If the average marks of all students in that class is 50, then the percentage of boys present in the class is

Explanation

Official WBPSC key (Series A): (C) 80%. Average Marks of Boys and Girls Average marks of boys = 52 Average marks of girls = 42 Average marks of entire class = 50 Find the percentage of boys. Let: Number of boys = (B) Number of girls = (G) Using weighted average: {52B+42G}/{B+G}=50 Multiply both sides: 52B+42G=50B+50G 2B=8G B=4G Thus, B:G = 4:1 Total parts:[4+1=5] Percentage of boys: 4/5×100 =80%