Friday, April 3, 2009

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.
The term cross product can help me remember how to solve the proportion because all I have to do is multiply across and nothing else. Basically, all you have to do is multiply the numerator from the denominator from both of the ratios. Cross multiplying is easy because all you have to do is cross multiply, but if you have a variable in one of the ratios you have to figure out what is that variable. Furthermore, if one of the ratios has a variable and the other one does not then, you still need to figure out what is the variable to get you answer.

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

The error in these steps: 2/3=x/12; 2x=36; x=18, the person who did this problem did not show it's work. Even though, the person did not show his/her work, he/her did not cross multiply. The only thing that the person did was multiply by straight. So the person just basically did was 2*x=2x and 3*12=36. Then the person did 2x=36 and then the person divided by 2 and got 18, so x=18. Finally the way he would of gotten it right, if he was to do;
2          x
__ = ___  3x=24; 24/3=8; x=8
3         12

3. Show: How to use cross products to decide whether the ratios 6:45 and 2:15 are proportional.

6          2
__=  ___  2*45=90
45       15    6*15=90

90 and 90  is proportional.