GRE Sample Test 5 Quantitative Reasoning 2

To isolate a, divide both sides of the equation by 16 to arrive at: a = $\frac{64^b}{16}$ Next, express the bases in base-2. 64 = $2^6$, so the numerator = $(26)^b$ = $2^6 b$. Expressed in base-2, the denominator = $2^4$. So the equation simplifies to: a = $\frac{2^{6b}}{2^4}$ Since we’re dividing terms with the same base, we’ll keep the base and subtract the exponents to arrive at: $2^{6b-4}$.