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CEMC Gauss (Grade 8), 2019

Combinatorics Difficulty 1.2 Junior Find the answer Canada

Based on the graph shown, how many vehicles had an average speed of at least 80 km/h?

Figure 0

Pick one

Solution

When x=3x=3, 2xamp;=2×3=63x−1amp;=3×3−1=8x+5amp;=3+5=87−xamp;=7−3=46+2xamp;=6+2×3=12\begin{align*} 2x&=2\times3=6\\ 3x-1&=3\times3-1=8\\ x+5&=3+5=8\\ 7-x&=7-3=4\\ 6+2x&=6+2\times3=12 \end{align*} Of the given answers, 3x−1=83x-1=8 is the only one of the given equations which is true when x=3x=3.

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