Question 86262
At least you are givinig it a shot.  Here's my approach.  I would have thought the numbers of boys and girls would come out in whole numbers but they didn't.

Let x=number of male students
Then 1680-x=number of female students

Now we are told that 40% of the male students (0.40x) plus 25% of the female students (0.25(1680-x)) were in attendence and that amounted to 560 students.  So our equation to solve is:

0.40x+0.25(1680-x)=560  get rid of parens

0.40x+420-0.25x=560  subtract 420 from both sides

0.40x+420-420-0.25x=560-420  collect like terms

0.15x=140  divide both sides by 0.15

x=933.3333 or 933----------number of boys
1680-933=747--------------------------------number of girls

0.40(933)+0.25(747)=560

373+187=560
560=560


Hope this helps---ptaylor