00:01
So for this problem it tells us that students went out to dinner and paid $162, but we don't know how many students and we don't know how much they paid each.
00:12
But if i do n times d, so a number of students times however many dollars they paid each, that'll equal to 162.
00:24
Then they tell us that three of them forgot their money, and so the remaining had to put in $2 .7 .7.
00:32
So if i do n minus 3, so there's the three people forgot their money, times dollars plus 270, that still equals the 162.
00:47
So now what i'm going to do is use substitution.
00:51
So if i take this and i solve for n, n will equal 162 over d.
00:58
I'm going to take that and i'm going to fill it in for n here.
01:03
So that gives me 162 over d minus 3 times d plus 2 .7 equals 162.
01:16
Now i'm going to foil.
01:19
So 162 over d times d is just 162 plus 437 .4 over d minus 3d minus 8 .1 equals 162.
01:45
The 162 is will cancel.
01:48
So i'm left with 437 .4 over d minus 3d minus 8 .1 equals 0.
02:00
So now to get rid of the d on the bottom, if i multiply through by d, i get 437 .4 minus 3d squared minus 8 .1d equals zero.
02:14
Now that's a quadratic equation that i can solve, but because of the decimals and everything, the best way to solve this will be using the quadratic formula...