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Problem 83 Difficulty 1.2 Multiple choice CEMC Gauss (Grade 8) · Canada · 2019
Based on the graph shown, how many vehicles had an average speed of at least 80 km/h?
60 to 69 km per hour, 10
Pick one
A 45 45 45 B 15 15 15 C 35 35 35 D 70 70 70 E 50 50 50
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Official solution When x = 3 x=3 x = 3 2 x = 2 × 3 = 6 3 x − 1 = 3 × 3 − 1 = 8 x + 5 = 3 + 5 = 8 7 − x = 7 − 3 = 4 6 + 2 x = 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*} 2 x 3 x − 1 x + 5 7 − x 6 + 2 x = 2 × 3 = 6 = 3 × 3 − 1 = 8 = 3 + 5 = 8 = 7 − 3 = 4 = 6 + 2 × 3 = 12 3 x − 1 = 8 3x-1=8 3 x − 1 = 8 x = 3 x=3 x = 3
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