Of the last 20 balloons sold at a party store, 10 were blue. Considering this data, how many of the next 18 balloons sold would you expect to be blue?

9 blue balloons

Step-by-step explanation:

Let's create a proportion using the following set up.

blue balloons/total balloons=blue balloons/total balloons

We know that 10 blue balloons were sold if 20 total balloons were sold. We don't know how many blue are are sold if 18 total are sold. Therefore, we can say x blue are sold for 18 total sold.

10 blue/20 total=x blue/18 total

10/20=x/18

We want to find out what x is. In order to do this, we have to get x by itself. Perform the opposite of what is being done to the equation. Keep in mind, everything done to one side, has to be done to the other.

x is being divided by 18. The opposite of division is multiplication. Multiply both sides by 18.

18*(10/20)=(x/18)*18

18*(10/20)=x

18*1/2=x

9=x

If 18 balloons are sold, 9 blue balloons would be expected to be sold.