SAT Mathematics Practice Test 2

Subtracting 6 from each of $5\mathit{x}=6=10$ yields $5\mathit{x}=4$.Dividing both sides of $5\mathit{x}=4$ by 5 yields $\mathit{x}=\frac{4}{5}$.The value of x can now be substituted into the expression $10\mathit{x}+3$,giving $10\left(\frac{4}{5}\right)+3=11$ Alternatively, the expression $10+\mathit{x}$ can be rewritten as $2\left(5\mathit{x}+6\right)-9$, and 10 can be substituted for $5\mathit{x}+6$ giving $2\left(10\right)-9=11$
Choic A,B and D are incorrect. Each of these choices leads to $5\mathit{x}+6\ne 10$ contradicting the given equation, $5\mathit{x}+6=10$, For example, choice A is incorrect because if the value of $10\mathit{x}+3$ were 4, then it would follow that x = 0.1, and the value of $5\mathit{x}+6$ would be 6.5, not 10.