Lorri took a $240 \mathrm{~km}$ trip to Waterloo. On her way there, her average speed was $120 \mathrm{~km} / \mathrm{h}$. She was stopped for speeding, so on her way home her average speed was $80 \mathrm{~km} / \mathrm{h}$. What was her average speed, in $\mathrm{km} / \mathrm{h}$, for the entire round-trip?
(A) 90
(B) 96
(C) 108
(D) 102
(E) 110

## Part C: Each correct answer is worth 8.
Solution 1

Lorri's $240 \mathrm{~km}$ trip to Waterloo at $120 \mathrm{~km} / \mathrm{h}$ took $240 \div 120=2$ hours.

Lorri's $240 \mathrm{~km}$ trip home at $80 \mathrm{~km} / \mathrm{h}$ took $240 \div 80=3$ hours.

In total, Lorri drove $480 \mathrm{~km}$ in 5 hours, for an average speed of $\frac{480}{5}=96 \mathrm{~km} / \mathrm{h}$.

Solution 2

Lorri's $240 \mathrm{~km}$ trip to Waterloo at $120 \mathrm{~km} / \mathrm{h}$ took $240 \div 120=2$ hours.

Lorri's $240 \mathrm{~km}$ trip home at $80 \mathrm{~km} / \mathrm{h}$ took $240 \div 80=3$ hours.

Over the 5 hours that Lorri drove, her speeds were 120, 120, 80, 80, and 80, so her average speed was $\frac{120+120+80+80+80}{5}=\frac{480}{5}=96 \mathrm{~km} / \mathrm{h}$.

ANSWER: (B)