# How do you use cross products to solve 30/6=b/7?

Apr 11, 2018

$b = 35$

#### Explanation:

eliminate the denominators so that you can get an idea as to what b will become

$\frac{30}{6} = \frac{b}{7}$ cross multiply the denominators by the other numerators

$30 \left(7\right) = b \left(6\right)$

$210 = 6 b$ divide both sides by 6 to isolate b

$b = 35$

a faster way to do this is by seeing that $\frac{30}{6}$ equals $\frac{5}{1}$. take that $5$ and multiply it by $7$ to get $35$

Apr 11, 2018

$b = 35$

#### Explanation:

$\text{given equal fractions } \frac{a}{b} = \frac{c}{d}$

$\text{then "ad=bclarrcolor(blue)"cross product}$

$\text{using this method to solve the equation}$

$\Rightarrow 6 b = \left(30 \times 7\right)$

$\Rightarrow b = \frac{30 \times 7}{6} = 35$