00:01
So we have two unknowns.
00:02
The number of dress slacks and the number of casual slacks that the person is buying, dress slacks cost $40 each and casual ones cost $25 each.
00:13
We also know the total amount of money spent and the total number of slacks purchased.
00:18
This is a classic system of equations.
00:23
So for d, the number of them is 36.
00:26
So the dress slacks plus the casual slacks is 36 total slacks.
00:34
Now let's deal with the money.
00:37
$40 times how many dress slacks there are plus $25 times each casual pair of slacks.
00:49
The money total was $118 .5.
00:55
So system of equations.
00:57
The top equation is how many items and the bottom equation deals with the money.
01:02
This equation on the bottom, if you divide by five everywhere, it really becomes much easier.
01:15
Your top equation is d plus c equals 36.
01:19
If you do 40 divided by five, you get 8d.
01:22
25 divided by five is 5 c and 1185.
01:28
Divided by five is 2 .37.
01:32
Now you have smaller numbers.
01:34
And this top equation, if you go minus c on both sides, you get that d is 36 minus c.
01:44
So one thing we can do is substitute.
01:48
This is my d, and i'm going to plug that in for d right there.
01:54
Substitution method.
01:56
So now we're going to make our equation...