# SAT Practice Questions: Working with Supplementary Angles

When you run into a math question on the SAT where you need to work with supplementary angles, the special number to keep in mind is 180: this is how much supplementary angles total when you add them together.

In the following practice questions, you’re asked to combine this property of supplementary angles with some algebra to get your answers.

## Practice questions

**In the drawing,***l*_{1}is parallel to*l*_{2}. What is the value of*a*?

**A.**60 degrees

**B.**70 degrees

**C.**80 degrees

**D.**90 degrees**In the following image, the angles are supplementary. What is the value of***k*?

**A.**17

**B.**18

**C.**19

**D.**20

## Answers and explanations

**The correct answer is Choice (D).**

If*l*_{1}is parallel to*l*_{2}, all the acute angles are equivalent and all the obtuse angles are equivalent. This makes the angles marked*a*+*b*and*a*–*b*supplementary, meaning they total 180 degrees. Set up the equation and solve for*a*:

**The correct answer is Choice (C).**

Supplementary angles total 180 degrees. Add the angles and set them equal to 180: