Proportions

A proportion is when two ratios are equal to each other.

We can check to see if a proportion is equal by checking its cross products.

3/4 = 9/12

Multiply: 3 x 12 = 9 x 4

Both sides equal 36 so this is a legitimate proportion.


As we saw in class, though, you may have to solve for a variable.

3/4 = x/12

Multiply: 3 x 12 = 4x

36 = 4x

Divide each side by 4 to get the variable alone.

9 = x

Finish 6:2 tonight. Questions 1-7; 10-15; 18.