One day a store sold 21 sweatshirts. white ones cost $9.95 and yellow ones cost $ 11.50. in all, $235.30 worth of sweatshirts were sold. how many of each color were sold?

For this problem you have yo set up two equations.

White shirts = w Yellow shirts = y

1st: w + y = 21
2nd: 9.95w + 11.50y = 235.30

Now we're going to do system of equations using substitution.

If w + y = 21, then y = 21 - w
If y = 21 - w, then you can substitute this in the second equation for y.

9.95w + 11.50(21 - w) = 235.30
9.95w + 241.5 - 11.50w = 235.30
-1.55w + 241.5 = 235.30
-1.55w = -6.2
w = 4, so 4 whites shirt were sold.

Now I'm finding out how many yellow shirts were sold using one of the two equations at the top.

w + y = 21
4 + y = 21
y = 17

So 17 yellow shirts were sold and 4 white shirts were sold.