If 3x + 5 = 20, what is the value of x?
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Show answer and explanation
Answer: 5
Subtract 5 from both sides to get 3x = 15. Divide by 3, so x = 5.
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Build the SAT Math skill behind one-variable equations, slope-intercept form, systems, and equation word problems.
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Practice examples
If 3x + 5 = 20, what is the value of x?
Answer: 5
Subtract 5 from both sides to get 3x = 15. Divide by 3, so x = 5.
A line has equation y = 4x - 7. What is the y-value when x = 3?
Answer: 5
Substitute x = 3 into y = 4x - 7. That gives y = 4(3) - 7 = 12 - 7 = 5.
A tutor charges a fixed signup fee plus $18 per hour. A 5-hour session costs $115. What is the fixed signup fee?
Answer: $25
Let f be the fixed fee. The total cost is f + 18h. For 5 hours, f + 18(5) = 115, so f + 90 = 115 and f = 25.
Avoid these traps
Every addition, subtraction, multiplication, or division step has to preserve equality on both sides of the equation.
SAT questions often ask for a value like 2x, x + 3, or the y-value, not always x itself.
Negative constants and negative slopes are common traps. Rewrite the equation slowly before solving.
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FAQ
Linear equations show up often because they connect to algebra, word problems, graphs, systems, and function notation.
Move into systems of equations, functions, and algebra word problems so the same equation skills transfer into harder formats.
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