Mrs Ruiz has 11/12 yard of string to hang 3 banners. She uses the same length of string to hang each banner. How much string does she use for each banner?

She uses 11/36 yards of string for each.

In this problem, you're dividing the amount of string by the number of banners, so 11/12 : 3. To do this though, it's easiest to convert the 3 into a fraction. After you do this, you're left with:

11/12 : 3/1

When dividing fractions, you flip the second fraction upside down and change the operation to its opposite, which gives you:

11/12 * 1/3

Then you just multiply across. 11*1=11 and 12*3=36, so you're left with 11/36 yards of string.