# SAT Math Multiple Choice Question 655: Answer and Explanation

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**Question: 655**

**10.** The equation *y* = *kx* - 1, where *k* is a constant, describes a line in the *xy*-plane. If the graph of this line contains the point (*a*, *b*), where *a* and *b* are nonzero, what is the value of *k* in terms of *a* and *b*?

- A.
- B.
- C.
- D.

**Correct Answer:** A

**Explanation:**

**A**

**Algebra (linear equations) MEDIUM**

Original equation:

*y* = *kx* - 1

Substitute x 5 a and y 5 b:

*y* = *ka* - 1

Add 1:

*b* + 1 = *ka*

Divide by a: