Library / /219 of 428

, 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?

Hide/Reveal Description of Vehicles

60 to 69 km per hour, 10
70 to 79 km per hour, 20
80 to 89 km per hour, 15
90 to 99 km per hour, 30
100 to 109 km per hour, 5

Pick one

Solution

When $x=3$ , $\begin{align*} 2x&=2\times3=6\\ 3x-1&=3\times3-1=8\\ x+5&=3+5=8\\ 7-x&=7-3=4\\ 6+2x&=6+2\times3=12 \end{align*}$ Of the given answers, $3x-1=8$ is the only one of the given equations which is true when $x=3$ .

Figure for this problem

Want a route through all this instead of an archive? The track puts 2,604 problems in a working order, from Junior Challenge level to the IMO shortlist.

Source: CEMC, University of Waterloo, licensed CC-BY-NC-4.0. Statement reproduced verbatim; metadata (topic, difficulty) added by this project.