SAT Mathematics Practice Test 6

Substituting the given value of $\mathit{y}=18$ into the equation $\mathit{x}=\frac{2}{3}\mathit{y}$ yields $\mathit{x}=\left(\frac{2}{3}\right)\left(18\right)$,or $\mathit{x}=12$.. The value of the expression $2\mathit{x}-3$ when $\mathit{x}=12$ is $2\left(12\right)-3=21.$ Choice B is incorrect. If $2\mathit{x}-3=15$, then adding 3 to both sides of the equation and then dividing both sides of the equation by 2 yields $\mathit{x}=9$. Substituting 9 for x and 18 for y into the equation $\mathit{x}=\frac{2}{3}\mathit{y}$ yields $9=\frac{2}{3}18=12$,which is false. Therefore, the value of $2\mathit{x}-3$ cannot be15. Choices C and D are also incorrect. As with choice B, assuming the value of $2\mathit{x}\mathit{–}3$ is 12 or 10 will lead to a false statement.