Algebra 1a: Chapter 3, Lesson 9, page 148.
Proportions
A ratio of 2 quantities is a comparison, often expressed as a fraction. An equation that states that 2 ratios are equal is called a proportion. I prefer to just criss-cross, or cross multiply proportional problems, but the book’s way is OK too.
For example,
`x/63=2/9`, I solve by criss-crossing. That becomes
`x*9=2*63` or `9x=63*2` or `9x=126`
and dividing both sides by 9 to clear the x, gives us `x=14`.
Here is a link from purplemath.com that has some more examples.
Two of tonight’s homework problems solved by MrE are here! Just click it!