Set 11: Systems of Equations (Advanced)

Choice B is correct. Choice B is the correct answer. Let $n$ = notebooks and $p$ = pens. System: $\begin{cases} n + p = 25 \\ 3 n + 2 p = 65 \end{cases}$ Step 1: From first: $p = 25 - n$ Step 2: Substitute: $$$3n + 2(25 - n) = 653n + 50 - 2 n = 65$n = 15 Solution: 15 notebooks (and 10 pens) Verification: $15+ 10 = 25$ ✓ and $3(15) + 2(10) = 45 + 20 = 65$ ✓ Strategic Tip: One equation for quantity, one for total cost. Other choices fail verification.