AlgebraMediumSystem where one equation gives a substitution
Algebra practice question
If 5x + 2y = 23 and y = 3x − 4, what is the value of x?
Answer: 3
Substitute y = 3x − 4 into the first equation: 5x + 2(3x − 4) = 23 → 11x − 8 = 23 → 11x = 33 → x = 3.
Common wrong answers
- If you answered 1
- 1 comes from 5x + 6x + 8 = 23 → 11x = 15, mishandling the sign of −8.
- If you answered 5
- 5 is y, not x.
- If you answered 33
- 33 is 11x, before dividing by 11.
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