SAT Math Multiple Choice Practice Question 579: Answer and Explanation

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Question: 579

15. If ab = 119 and ab = 7, what is the value of a ?

A. 5
B. 12
C. 14
D. 17
E. 21

Correct Answer: B

Explanation:

B We've got some quadratic equations here. The expression a2b2 can be factored into (a + b)(ab). The question tells us that ab = 7, so we can replace that quantity in the factored equation: (a + b) × 7 = 119, so a + b = 17. We need to find the value of a, and we can use simultaneous equations. If we stack and add the equations, the b-values cancel out:

so a = 12, as seen in B.

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