Question 131413
Ok, start by assigning variables to the unknown quantities:
Let B = the number of boys and G = the number of girls.
From the problem description, you can write:
1) G+B = 25 "In a class of 25 students,..." and...
2) G = B+7 "...there are 7 more girls than boys."
Now you substitute the second equation (G = B+7) for the G in the first equation (G+B = 25) and solve for  B.
{{{(B+7)+B = 25}}} Combine like-terms.
{{{2B+7 = 25}}} Subtract 7 from both sides.
{{{2B = 18}}} Finally, divide both sides by 2.
{{{B = 9}}} So there are 9 boys in the class.
{{{G = B+7}}}
{{{G = 9+7}}}
{{{G = 16}}} and there are 16 girls in the class.