GRE Sample Test 4 Quantitative Reasoning 1

Henry purchased x apples, and Jack purchased 10 apples less than one-third the number of apples Henry purchased. One-third of means the same as one-third times, and the number of apples Henry purchased is x. Thus, this boils down to
J = $\frac{1}{3}\mathit{x}-10$.
You can plug this in for Quantity A. We have $\frac{1}{3}\mathit{x}-10$ in Quantity A and $\frac{\mathit{x}-30}{3}$ in Quantity B. Now you can clear the fraction in Quantity B. Let’s split Quantity B into two fractions:
$\frac{\mathit{x}}{3}-\frac{30}{3}$. Leave the $\frac{\mathit{x}}{3}$ alone and cancel the factor of 3 from the numerator and denominator of $\frac{30}{3}$ and you’re left with $\frac{\mathit{x}}{3}-10$. What's $\frac{\mathit{x}}{3}$ ? It’s onethird of x. So Quantity A equals $\frac{1}{3}\mathit{x}-10$, while Quantity B also equals $\frac{1}{3}\mathit{x}-10$, and the answer is (C).