If 5x - 8 = 2x + 13, what is the value of 6x? | SAT Linear equations in one variable Question, Answer Explained

Math · AlgebraMedium

If $5x - 8 = 2x + 13$ , what is the value of $6x$ ?

$7$

$10$

$18$

$42$

Show answer and explanation

Answer: D

Subtract $2x$ from both sides: $3x - 8 = 13$ . Add $8$ to both sides: $3x = 21$ , so $x = 7$ . Then $6x = 6(7) = 42$ .

Choice A is the value of $x$ , but the question asks for $6x$ .

Why the other choices are wrong

A. 7 is the value of x. Multiply by 6 to get 6x.
B. This subtracts 8 from 13 instead of adding 8 to both sides, which gives 3x = 5.
C. This adds 2x to both sides instead of subtracting it, which gives 7x = 21 and x = 3.

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