In a math exam, the average score of 6 1 class is 9 1. The average score of boys is 89, and that of girls is 92.5. There are 24 girls and how many boys?

Method 1.

The average score of girls is above: (92.5-9 1) times 24=36.

Every boy is below average: 9 1-89=2.

The total score of boys is lower than the average = the total score of girls is higher than the average.

So the number of boys; 36/2= 18

Method two.

Let the number of boys be x.

Then (9 1-89)X=(92.5-9 1) times 24.

X= 18

Method three.

Let the number of boys be x.

Then 89X+92.5 times 24=9 1 times (X+24).

X= 18