SAT Mathematics Practice Test 3

One of the three numbers is x;
let the other two numbers be y and z.
Since the sum of three numbers is 855, the equation x + y + z = 855 is true.
The statement that x is 50% more than the sum of the other two numbers can be represented as $\mathit{x}=1.5\left(\mathit{y}+\mathit{z}\right)$,or $\frac{\mathit{x}}{1.5}=\mathit{y}+\mathit{z}$.
Substituting $\frac{\mathit{x}}{1.5}$ for $\mathit{y}+\mathit{z}$ in $\mathit{x}+\mathit{y}+\mathit{z}=885$ gives $\mathit{x}+\frac{\mathit{x}}{1.5}=855$
This last equation can be rewritten as $\mathit{x}+\frac{2\mathit{x}}{3}=855$ or $\frac{5\mathit{x}}{3}$
Therefore, $\mathit{x}$ equals $\frac{3}{5}\times 855=513$
Choices A, C, and D are incorrect and may be the result of calculation errors.