4/3/09
Aim: How do we solve proportions by using cross products?
The term cross product can help you remember how to solve a proportion, by dividing the product by the number.
Example:
2 x
___ = ___ ; 2x = 36; x =18.
3 12
He did this problem wrong because if you cross multiply you're going to get 3x= 24. If you subtract 3 from 24 you're going to have 21. So he put x= 18, but it was x= 7. I know x=7 also because 21÷3 is 7.
Problem:
6 2
___= ___
45 15
Aim: How do we solve proportions by using cross products?
The term cross product can help you remember how to solve a proportion, by dividing the product by the number.
Example:
2 x
___ = ___ ; 2x = 36; x =18.
3 12
He did this problem wrong because if you cross multiply you're going to get 3x= 24. If you subtract 3 from 24 you're going to have 21. So he put x= 18, but it was x= 7. I know x=7 also because 21÷3 is 7.
Problem:
6 2
___= ___
45 15
15 • 6= 90 , 45 • 2= 90 So it's 90 = 90 This problem is Proportional.
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