Question 170726
alright so we would normally find out an average cost per person by taking the cost and dividing by number of people....lets call the original  # of people attending x so avg cost would be 500/x  but now x is decreasing by 5 and the average cost is increasing by 5 so
:
{{{500/x=(500/(x-5)-5)}}} mulitply all terms by x(x-5)
:
{{{500(x-5)=500x-5x^2+25x}}}
:
500x-2500=500x-5x^2+25x}}}
:
{{{5x^2-25x-2500=0}}}divide by 5
:
{{{x^2-5x-500=0}}}
:
{{{system(x=25,x=-20)}}}
:
throw out the negative and we have the original amount of people of 25
:
therefore the number of people attending the party is{{{highlight(25-5=20)}}}

:
*[invoke quadratic "x", 1, -5, -500]