RICAS Grades 6-8 Ratios and Proportional Relationships. Practice it free.

Use a conversion factor with centimeters in the numerator so millimeters cancel: $80 \text{ mm} \times \dfrac{1 \text{ cm}}{10 \text{ mm}} = 8 \text{ cm}$.

Three gallons of water is $3 \times 16 = 48$ cups. With a $7$ to $56$ ratio, $\dfrac{7}{56} = \dfrac{x}{48}$, so $56x = 336$ and $x = 6$ cups of concentrate.

$\dfrac{4}{5} = 0.8 = 80\%$.

Convert $45\%$ to a decimal and multiply: $0.45 \times 360 = 162$ chairs.

Discount: $\frac{25}{100} \times \text{\char36}200 = \text{\char36}50$. Sale: $\text{\char36}200 - \text{\char36}50 = \text{\char36}150$.

Increase $= 13{,}800 - 12{,}000 = 1{,}800$. Percent increase $= \dfrac{1{,}800}{12{,}000} = 0.15 = 15\%$.

Scale the ratio: $32$ oz red is $8$ groups of $4$, so blue paint = $8 \times 7 = 56$ ounces.

Cross-multiply: $9 x = 63 \cdot 6 = 378$. So $x = 42$.