AlgebraEasy–MediumSubstitution with y given as a multiple of x
Algebra practice question
If y = 3x and x + y = 16, what is the value of x?
Answer: 4
Substitute y = 3x into the second equation: x + 3x = 16, so 4x = 16 and x = 4. (Then y = 12.)
Common wrong answers
- If you answered 8
- 8 is 16/2, treating x + y as 2x. Since y = 3x, x + y is 4x.
- If you answered 12
- 12 is y. The question asks for x.
- If you answered 5.33
- 5.33 is 16/3, dividing by the 3 alone; x + 3x = 4x.
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