Posted by **JERSEYGIRL** on Sunday, December 4, 2011 at 8:49pm.

40 =15

x x - 20 This is a three part question>> first find the lcd method of solving this equations, and the second ones about cross-multiplying method to solve this equations ,The next question asked would the cross- multiplying method work for all rational equations?? Explain.

- Algebra -
**Reiny**, Sunday, December 4, 2011 at 9:02pm
I am guessing you are trying to type the equation

40/x = 15/(x-20)

The LCD is x(x-20_

so

40/x (x(x-20)) = 15/(x-20) (x(x-20))

40(x-20) = 15x

40x - 800 = 15x

25x = 800

x = 32

cross-multplying gets you directly to

40(x-20) = 15x

etc

Cross-multiplying only works if your equation contains a single term on the left and a single term on the right,

that is,

you have to add/subract the terms first if you have more than one.

In that case I simply multiply each term by the LCD, to get rid of my fractions.

- Algebra -
**JERSEYGIRL**, Sunday, December 4, 2011 at 9:42pm
(1)40 =15 (2) x - 20 (2 DIFFERENT EQUATIONS)????? help please!!!!

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