AlgebraMediumChange in y for a given change in x along a line
Algebra practice question
In the xy-plane, a point moves along the line 5x + 2y = 20 so that its x-coordinate increases by 4. By how much does its y-coordinate change?
Answer: -10
Solve for y: y = −(5/2)x + 10, so the slope is −5/2. An increase of 4 in x changes y by (−5/2)(4) = −10.
Common wrong answers
- If you answered 10
- 10 has the wrong sign; y decreases as x increases.
- If you answered -2.5
- −2.5 is the change for an increase of 1 in x.
- If you answered -20
- −20 uses a slope of −5 instead of −5/2.
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