Math Gold Medalist

Lor

2023 AMC 8 

Problem 9

Malaika is skiing on a mountain. The graph below shows her elevation, in meters, above the base of the mountain as she skis along a trail. In total, how many seconds does she spend at an elevation between $4$ and $7$ meters?[asy] // Diagram by TheMathGuyd. Found cubic, so graph is perfect. import graph; size(8cm); int i; for(i=1; i<9; i=i+1) { draw((-0.2,2i-1)--(16.2,2i-1), mediumgrey); draw((2i-1,-0.2)--(2i-1,16.2), mediumgrey); draw((-0.2,2i)--(16.2,2i), grey); draw((2i,-0.2)--(2i,16.2), grey); } Label f;  f.p=fontsize(6);  xaxis(-0.5,17.8,Ticks(f, 2.0),Arrow());  yaxis(-0.5,17.8,Ticks(f, 2.0),Arrow());  real f(real x)  {  return -0.03125 x^(3) + 0.75x^(2) - 5.125 x + 14.5;  }  draw(graph(f,0,15.225),currentpen+1); real dpt=2; real ts=0.75; transform st=scale(ts); label(rotate(90)*st*"Elevation (meters)",(-dpt,8)); label(st*"Time (seconds)",(8,-dpt)); [/asy]$\textbf{(A)}\ 6 \qquad \textbf{(B)}\ 8 \qquad \textbf{(C)}\ 10 \qquad \textbf{(D)}\ 12 \qquad \textbf{(E)}\ 14$

Drawing on the Graph

Draw to horizontal lines ( y = 3 and y= 7) and consider the region between them.

   Solution