What percent of 7.2 is 45?

Jun 30, 2018

625%

Explanation:

Let the unknown percentage be $x$ giving:

x%xx7.2=45

The % symbol is like a unit of measurement but one that is worth $\frac{1}{100}$ so:

color(green)(color(red)(x%)xx7.2=45 color(white)("d") ->color(white)("d")[color(red)(x xx1/100)]xx7.2=45)

color(white)("ddddddddddddd")->color(white)("dddd")color(green)(color(red)(x/100)color(white)("ddd")xx7.2=45)

Divide both sides by $7.2$ ('gets rid' of it from the left)

$\frac{x}{100} = \frac{45}{7.2}$

Multiply both sides by 100 ('gets rid' of it from the left)

$x = 100 \times \frac{45}{7.2}$

$x = 625$

But this id the numerator of a percentage so we have:

$\frac{625}{100} \textcolor{w h i t e}{\text{d")->color(white)("d")625color(white)("d.}} \underbrace{\times \frac{1}{100}}$
$\textcolor{w h i t e}{\text{dddddddddddd.dd}} \downarrow$

color(white)("dddd")->color(white)("d")625 color(white)("ddd.")%

625%

Jun 30, 2018

$625$

Explanation:

$\frac{7.2}{100} \cdot x = 45$

$x = 45 \cdot \frac{100}{7.2} = \frac{4500}{7.2} = \frac{45000}{72} = \frac{5000}{8} = 625$