Think & DIscuss.

Aim: How do we solve proportions by using cross products?

1. Explain how the term cross product can help you remember how to solve a proportion.

2. Describe the error in these steps: 2/3 = x/12 ; 2x= 36; x=18.

3. Show how to use cross products to decide whether the ratios 5:45 and 2:15 are proportional.

____________________________________________________________________

1.  3/12 and x/16

Step 1: Cross Multiply. ;3 x 16=48 and 12 x X=?

Step 2: Divide 12 into 48 which equal 4.

Step 3: Check your work by cross multiplying . 3x16=48 and 12x4=48. This problem is proportional. 

2.  The things that this person did wrong in the problem was that they multiplied 12x3 and that gave a answer of 36 then they divided 2 into 36 and the answer was 18. 

3.  The ratios 5:45 and 2:15 are not proportional because when you cross multiply 5x15=75 and 45x2=90 so that means that 5:45 and 2:15 is not proportional.