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4-58.

Ms. B is making snickerdoodle cookies. Her recipe uses one-and-a-half teaspoons of cinnamon to make two-dozen cookies. If she needs to make thirteen-dozen cookies in order to give one cookie to each of her students, how much cinnamon will she need?

Use proportions to solve this problem. Assign a variable to the unknown number of teaspoons of cinnamon.
For this case, we will use the variable $n$.

Multiply both sides by $2$.

Multiply both sides by $13$.

Divide by 2 on both sides.

Remember to use the conversion factor to determine how many tablespoons and teaspoons Ms. B will need.

$\frac{ 1 \frac{ 1 }{2 } \text{ teaspoons}}{ 2\text{ dozen cookies}}= \frac{ n\text{ teaspoons}}{ 13\text{ dozen cookies}}$

$\frac{ 1 \frac{ 1 }{2 } }{2 }= \frac{ n }{13 }$

$1 \frac{ 1 }{2 } = \frac{ 2n }{13 }$

$19.5 = 2n$

$n=9.75 \text{ or }9 \frac{3}{4} \text{ teaspoons}$