Question

How to do proportions?

Answer 1

Solving proportions is simply a matter of stating the ratios as fractions, setting the two fractions equal to each other, cross-multiplying, and solving the resulting equation. You'll probably start out by just solving proportions, like this: Find the unknown value in the proportion: 2 : x = 3 : 9.

Answer 2

 A proportion is just two fractions set equal to each other

So, when solve a proportion, you cross multiply

$\frac{x}{3}$ = $\frac{3}{4}$

So, multilpy the top of the fraction on the left by the bottom of the fraction on the right

x · 4 = 4x

Now, multiply the bottom of the left by the top of the right

3 · 3 = 9

Now, set these two products equal to each other

4x = 9

Divide by 4 to isolate x

x = $\frac{9}{4}$