One yard of ribbon costs [tex]$3 \frac{1}{2}$[/tex] dollars. How much does each length of ribbon cost if each one is [tex]\frac{5}{8}[/tex] yards?

We can set up a ratio for this problem. We have that one yard of ribbon costs 3 1/2 dollars, or $3.50. We want to know how much 5/8 of the ribbon costs. We can set up a ratio!

The top of our ratio will be amount in yards, and the bottom will be the cost of that amount.

Known:

Amount/Cost= (1 yd)/($3.50)

Unknown:

Amount/Cost= (5/8 yd)/(?)

We have a question mark here to symbolize the unknown cost of 5/8 of a yard.

Now we have two ratios. We can set them equal to eachother.

(1 yd)/($3.50)=(5/8 yd)/(?)

We can use algebraic rules or cross multiply and we get that ? = $2.1875

This means that each 5/8 of a yard is $2.19 rounded to two significant figures.

Here are the instructions for cross multiplying:

Above the unknown number, in this case ?, multiply that number by the diagonal number. This would be (5/8) x (3.5). This equals 2.1875. Then, divide that number by the number diagonal from the unknown, ?. In this case it is just 1, and 2.1875/1 is equal to 1.

This is one way to solve for the unknown.