Question 1: Problem Solving
Easy · First-Degree Equations
If x is a number such that 5(x − 2) = 3x + 8, what is the value of x?
- A. −1
- B. 5
- C. 9
- D. 17
- E. 18
Show the answer and explanation
Answer: C. 9
- A. This comes from writing 2x = 8 − 10 instead of 2x = 8 + 10, moving the −10 across the equals sign without changing its sign.
- B. This follows from reading 5(x − 2) as 5x − 2, which gives 2x = 10 and x = 5. The 5 must multiply both terms in the bracket.
- C. Correct. 5x − 10 = 3x + 8 reduces to 2x = 18, so x = 9.
- D. This treats the right-hand side as 3(x + 8), giving 5x − 10 = 3x + 24 and x = 17. There is no bracket on the right.
- E. 18 is the value of 2x, the last line before dividing by 2.
How to solve it
Distributing on the left gives 5x − 10 = 3x + 8. Subtracting 3x from both sides gives 2x − 10 = 8, and adding 10 gives 2x = 18, so x = 9.
