Set 13: Systems of Equations (Advanced)

Choice B is correct. Choice B is the correct answer. Let $s$ = swimmer speed in still water and $c$ = current speed. System: $\begin{cases} (s + c) \cdot 1 = 6 \\ (s - c) \cdot 2 = 6 \end{cases}$ Step 1: Simplify: $\begin{cases} s + c = 6 \\ s - c = 3 \end{cases}$ Step 2: Add equations: 2s = 9$s = 4.5$$ Step 3: Find $c$: 4.5+ c = 6c = 1.5$$ Solution: Current is 1.5 mph Verification: Down: (4.5 + 1.5) \times 1 = 6$✓, Up:$(4.5 - 1.5) \times 2 = 6$ ✓ Strategic Tip: Current aids downstream, opposes upstream. Other choices fail verification.