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Mathematics 20 Online
OpenStudy (prominer10000):

What is the ratio of x to y? 3/2 = 2x/2x+y A. -3/2 B. -2/3 C. 2/3 D. 3/2 If you're confused of what the equation is, let me know and I'll take a screenshot of the question so it's easier. But, I'm thinking it's C.

OpenStudy (phi):

is it \[ \frac{3}{2} = \frac{2x}{2x+y} \]?

OpenStudy (prominer10000):

@phi Yes it is.

OpenStudy (phi):

if you cross multiply, what do you get ?

OpenStudy (prominer10000):

x = 3y/2 y= 2x/3

OpenStudy (phi):

try this multiply both sides of \[ \frac{3}{2} = \frac{2x}{2x+y} \] by 2(2x+y)

OpenStudy (prominer10000):

So like this? 3 * 2x + y = 2 * 2x

OpenStudy (phi):

almost, you need parens 3*(2x+y)= 4x now distribute the 3

OpenStudy (prominer10000):

What do you mean distribute the 3?

OpenStudy (phi):

3*(2x+y) means 3 times each term inside the parens

OpenStudy (prominer10000):

Sorry, I'm a bit confused but I got this when I times 3 by the terms in the parentheses. y = 2x -3

OpenStudy (phi):

3*(2x+y)= 4x do 3*2x and 3*y

OpenStudy (phi):

think of (2x+y) as a "package" and you have 3 packages (so you have 3 of everything inside the package)

OpenStudy (prominer10000):

But how can I multiply it if I don't know what the variables are?

OpenStudy (phi):

you multiply letters by just showing them being multiplied example: x times y is x*y or xy obviously we don't know what number that is, but we do know that it means x times y

OpenStudy (phi):

3*(2x+y)= 4x now distribute the 3 (i.e. multiply each term inside by 3)

OpenStudy (prominer10000):

So 3 x (2xy) ?

OpenStudy (phi):

if it helps say you had 3 farms, each had 2 cows and 1 horse how many cows and horses do you have?

OpenStudy (prominer10000):

9?

OpenStudy (phi):

how many of each type ?

OpenStudy (prominer10000):

6 cows and 3 horses.

OpenStudy (phi):

yes you did 3( 2 cows + 1horse) and got 3*2 cows + 3*1 horse

OpenStudy (phi):

if we count x's and y's 3(2x + 1y) = 3*2 x + 3*1 y or 6x+3y

OpenStudy (phi):

see if you make sense of that. meanwhile 3*(2x+y)= 4x 6x+3y= 4x now add -4x to both sides 6x-4x + 3y = 4x - 4x on the right side, you have 4x take away 4 x's on the left you have 6 x's take away 4 x's (or cows if you like) that gives you 2x+3y= 0

OpenStudy (prominer10000):

So what do I do from here since I now have 0?

OpenStudy (phi):

we want the ratio of x to y or x/y so divide both sides by y \[ \frac{2x+3y}{y}= \frac{0}{y} \\ \frac{2x}{y} + 3\frac{y}{y}= 0 \]

OpenStudy (phi):

y/y is 1 so we have \[ 2 \frac{x}{y}+3=0 \] add -3 to both sides to get \[ 2 \frac{x}{y}=-3\] now divide both sides by 2

OpenStudy (phi):

we could also do this 2x+3y= 0 3y= -2x (add -2x both sides) now divide both sides by y 3 = -2 (x/y) now divide both sides by -2 (3/-2) = x/y or x/y = -3/2

OpenStudy (prominer10000):

So the answer is A?

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