Algebra
posted by JERSEYGIRL .
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 crossmultiplying method to solve this equations ,The next question asked would the cross multiplying method work for all rational equations?? Explain.

I am guessing you are trying to type the equation
40/x = 15/(x20)
The LCD is x(x20_
so
40/x (x(x20)) = 15/(x20) (x(x20))
40(x20) = 15x
40x  800 = 15x
25x = 800
x = 32
crossmultplying gets you directly to
40(x20) = 15x
etc
Crossmultiplying 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. 
(1)40 =15 (2) x  20 (2 DIFFERENT EQUATIONS)????? help please!!!!