MathDB
2015 AMC 8 #19

Source:

November 25, 2015
AMC 8coordinatePick's theorembarycentric coordinates

Problem Statement

A triangle with vertices as A=(1,3)A=(1,3), B=(5,1)B=(5,1), and C=(4,4)C=(4,4) is plotted on a 6×56\times5 grid. What fraction of the grid is covered by the triangle?
<spanclass=latexbold>(A)</span>16<spanclass=latexbold>(B)</span>15<spanclass=latexbold>(C)</span>14<spanclass=latexbold>(D)</span>13<spanclass=latexbold>(E)</span>12<span class='latex-bold'>(A) </span>\frac{1}{6} \qquad <span class='latex-bold'>(B) </span>\frac{1}{5} \qquad <span class='latex-bold'>(C) </span>\frac{1}{4} \qquad <span class='latex-bold'>(D) </span>\frac{1}{3} \qquad <span class='latex-bold'>(E) </span>\frac{1}{2}
[asy]
draw((1,0)--(1,5),linewidth(.5)); draw((2,0)--(2,5),linewidth(.5)); draw((3,0)--(3,5),linewidth(.5)); draw((4,0)--(4,5),linewidth(.5)); draw((5,0)--(5,5),linewidth(.5)); draw((6,0)--(6,5),linewidth(.5)); draw((0,1)--(6,1),linewidth(.5)); draw((0,2)--(6,2),linewidth(.5)); draw((0,3)--(6,3),linewidth(.5)); draw((0,4)--(6,4),linewidth(.5)); draw((0,5)--(6,5),linewidth(.5)); draw((0,0)--(0,6),EndArrow); draw((0,0)--(7,0),EndArrow); draw((1,3)--(4,4)--(5,1)--cycle); label("yy",(0,6),W); label("xx",(7,0),S); label("AA",(1,3),dir(230)); label("BB",(5,1),SE); label("CC",(4,4),dir(50)); [/asy]