## solving for x in following proportion

Simplificatation, evaluation, linear equations, linear graphs, linear inequalities, basic word problems, etc.

### solving for x in following proportion

i am a beginner in algebra. i need to solve this. x+15 divided by 5 = x+3 divided by 3
losdawg25

Posts: 1
Joined: Thu Feb 05, 2009 2:23 pm

losdawg25 wrote:i am a beginner in algebra. i need to solve this. x+15 divided by 5 = x+3 divided by 3

A basic property of proportions is that, if you "cross-multiply", you'll get the same value on either side. For instance:

. . . . .$\frac{1}{2}\, =\, \frac{3}{6}$

...can be "proved" by showing that 1(6) equals 3(2). Using this "cross-multiplication" fact to solve looks like this example:

. . . . .$\frac{2}{5}\, =\, \frac{x}{10}$

. . . . .$2(10)\, =\, x(5)$

. . . . .$20\, =\, 5x$

. . . . .$\frac{20}{5}\, =\, x\, =\, 4$

. . . . .$\frac{x\, +\, 15}{5}\, =\, \frac{x\, +\, 3}{3}$

...which "cross-multiplies" as:

. . . . .$(x\, +\, 15)(3)\, =\, (x\, +\, 3)(5)$

Multiply things out, and solve the resulting linear equation for the value of "x".

Eliz.

stapel_eliz

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Joined: Mon Dec 08, 2008 4:22 pm