Solving Proportions

In this video, we will be learning how to solve proportions using cross-multiplication.

For Example: $\frac{3}{5}=\frac{x}{14}\leftarrow$ First we cross-multiply $\frac{42}{5}=\frac{5x}{5}\leftarrow$ Then we divide by 5 to isolate x $x=\frac{42}{5}$

Video-Lesson Transcript

In this video, we will be learning how to solve proportions using cross-multiplication.

Ratio = Ratio $\dfrac{1}{4} = \dfrac{2}{8}$

Or $\dfrac{3}{5} = \dfrac{9}{15}$

Solving Proportions comes in when there is an unknown.

Let’s say we have $\dfrac{3}{5} = \dfrac{x}{15}$

We have to cross-multiply. $3 \times 15 = 45$ then $5 \times x = 5x$

We have $45 = 5x$

Then we get the value of $x = 9$ But what about it is not a perfect multiplier?

For example, $\dfrac{3}{5} = \dfrac{x}{14}$

In this case, we cross-multiply $3 \times 14 = 42$ then $x \times 5 = 5x$

So we have $x = \dfrac{42}{5}$

Here we have to $42\div {5}$

So $x = 8.4$

Here’s another example. $\dfrac{2}{5} = \dfrac{x + 1}{9}$

Let’s cross-multiply, $2 \times 9 = 18$ then $5 (x + 1)$

We have to distribute $18 = 5x + 5$

And we’ll have $13 = 5x$

To get the value of $x$ we have to $13\div 5$

Our final answer is $x = 2.6$