Official Guide Explanation:
Problem Solving #196

Background

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Solution and Metadata

Question: 196
Page: 180
Difficulty: 5 (Moderate)
Category 1: Algebra > Linear Equations-Two Unk >
Category 2: Word Problems > Data Interpretation >

Explanation: The chart gives you three equations: x + y = 80, y + z = 120, and x + z = 160. With three variables and three equations, it's just a matter of combining the equations to find z, the number of green marbles in jar R. Start by combining the first two equations by setting each one equal to y:

y = 80 - x

y = 120 - z

80 - x = 120 - z

z - x = 40

Now, combine this equation with the third equation by adding them:

x + z = 160

(-x) + z = 40

2z = 200

z = 100, choice (D).

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